U.S. patent application number 14/857023 was filed with the patent office on 2017-03-23 for power conversion apparatus and method for controlling power conversion apparatus.
The applicant listed for this patent is DENSO CORPORATION. Invention is credited to Shinya GOTO, Yuuichi HANDA, Seiji IYASU, Katsutoyo MISAWA, Kimikazu NAKAMURA, Kenji TOMITA.
Application Number | 20170085181 14/857023 |
Document ID | / |
Family ID | 58283257 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170085181 |
Kind Code |
A1 |
TOMITA; Kenji ; et
al. |
March 23, 2017 |
POWER CONVERSION APPARATUS AND METHOD FOR CONTROLLING POWER
CONVERSION APPARATUS
Abstract
A power conversion apparatus supplies power from a DC power
supply to a capacitive load by a current input push-pull DCDC
converter provided with switching elements Q1 and Q2. When a
capacitive load voltage is not larger than a second predetermined
value, a first mode is used which turns ON one of the switching
elements Q1 and Q2 alternated with turning OFF both. When the
capacitive load voltage is larger than the second predetermined
value but not larger than a first predetermined value, a second
mode is used which turns ON both of the switching elements Q1 and
Q2, then turns ON one of them, then turns OFF both, sequentially.
When the capacitive load voltage is larger than the first
predetermined value, a third mode is used, turning ON both of the
switching elements Q1 and Q2 alternated with turning ON one of
them.
Inventors: |
TOMITA; Kenji; (Nukata-gun,
JP) ; NAKAMURA; Kimikazu; (Handa-shi, JP) ;
GOTO; Shinya; (Gifu-shi, JP) ; MISAWA; Katsutoyo;
(Kariya-shi, JP) ; HANDA; Yuuichi; (Anjo-shi,
JP) ; IYASU; Seiji; (Anjo-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO CORPORATION |
Kariya-city, Aichi-pref. |
|
JP |
|
|
Family ID: |
58283257 |
Appl. No.: |
14/857023 |
Filed: |
September 17, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 3/3378 20130101;
H02M 3/33507 20130101 |
International
Class: |
H02M 3/335 20060101
H02M003/335 |
Claims
1. A power conversion apparatus, comprising: a direct current power
supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting one of an ON signal for instructing state transition
to ON, and an OFF signal for instructing state transition to OFF,
to the first and second switching elements, wherein the center tap
is connected to a negative terminal of the direct current power
supply and the predetermined connecting point is connected to an
output terminal of the choke coil, when the capacitive load voltage
is not larger than a first predetermined value, a first mode is
defined as a control under which a control of turning ON one of the
first and second switching elements and turning OFF the other
switching element is alternated with a control of turning OFF both
the first and second switching elements, and when the capacitive
load voltage is larger than the first predetermined value, a third
mode is defined as a control under which a control of turning ON
one of the first and second switching elements and turning OFF the
other switching element is alternated with a control of turning ON
both the first and second switching elements.
2. A power conversion apparatus, comprising: a direct current power
supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting one of an ON signal for instructing state transition
to ON, and an OFF signal for instructing state transition to OFF,
to the first and second switching elements, wherein the center tap
is connected to a negative terminal of the direct current power
supply and the predetermined connecting point is connected to an
output terminal of the choke coil, when the capacitive load voltage
is not larger than a second predetermined value that is a value
smaller than a first predetermined value, a first mode is defined
as a control under which a control of turning ON one of the first
and second switching elements and turning OFF the other switching
element is alternated with a control of turning OFF both the first
and second switching elements, when the capacitive load voltage is
larger than the second predetermined value but not larger than the
first predetermined value, a second mode is defined as a control
under which a control of turning ON both the first and second
switching elements, a control of turning ON one of the first and
second switching elements and turning OFF the other switching
element, and a control of turning OFF both the first and second
switching elements are sequentially repeated, and when the
capacitive load voltage is larger than the first predetermined
value, a third mode is defined as a control under which a control
of turning ON one of the first and second switching elements and
turning OFF the other switching element is alternated with a
control of turning ON both the first and second switching
elements.
3. The power conversion apparatus according to claim 1, wherein the
pulse generation unit transmits signals having an equal control
cycle to the respective first and second switching elements.
4. A power conversion apparatus, comprising: a direct current power
supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting a first PWM signal and a second PWM signal having an
equal control cycle and serving as driving signals for the
switching elements, the first PWM signal being transmitted to the
first switching element, the second PWM signal being transmitted to
the second switching element, wherein the center tap is connected
to a negative terminal of the direct current power supply and the
predetermined connecting point is connected to an output terminal
of the choke coil, when the capacitive load voltage is not larger
than a first predetermined value, a first mode is defined as a
control under which a phase difference between the first and second
PWM signals corresponds to a half of the control cycle and Duty
values of the first and second PWM signals are an equal of less
than 0.5, and when the capacitive load voltage is larger than the
first predetermined value, a third mode is defined as a control
under which a phase difference between the first and second PWM
signals corresponds to a half of the control cycle and Duty values
of the first and second PWM signals are an equal of larger than
0.5.
5. A power conversion apparatus, comprising: a direct current power
supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting a first PWM signal and a second PWM signal having an
equal control cycle and serving as driving signals for the
switching elements, the first PWM signal being transmitted to the
first switching element, the second PWM signal being transmitted to
the second switching element, wherein the center tap is connected
to a negative terminal of the direct current power supply and the
predetermined connecting point is connected to an output terminal
of the choke coil, when the capacitive load voltage is not larger
than a second predetermined value that is smaller than a first
predetermined value, a first mode is defined as a control under
which a phase difference between the first and second PWM signals
corresponds to a half of the control cycle and Duty values of the
first and second PWM signals are an equal in value and less than
0.5, when the capacitive load voltage is larger than the second
predetermined value but not larger than the first predetermined
value, a second mode is defined as a control under which a phase
difference between the first and second PWM signals corresponds to
on control cycle, the first and second PWM signals are signals
where a signal of a first Duty value is alternated with a signal of
a second Duty value different from the first Duty value on a
control-cycle basis, a result of adding the first Duty value and
the second Duty value is smaller than 1, and a time point of
switching the signal of the first Duty value from OFF to ON and a
time point of switching the signal of the second Duty value from
OFF to ON have a difference corresponds to one control cycle, and
when the capacitive load voltage is larger than the first
predetermined value, a third mode is defined as a control under
which a phase difference between the first and second PWM signals
corresponds to a half of the control cycle and Duty values of the
first and second PWM signals are an equal value if larger than
0.5.
6. The power conversion apparatus according to claim 4, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the first predetermined value is calculated from Formula
(1) V1=N.times.Vin/(2.times.(1-Duty0)) (1), where the V1 is the
first predetermined value, the N is a turn ratio of the second coil
to the first coil, the Vin is an input voltage detected by the
input voltage detecting means, and the Duty0 is an initial value of
the Duty value in starting control of the third mode, the initial
value being more than 0.5 but less than 1.
7. The power conversion apparatus according to claim 4, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the Duty value of the third mode when the capacitive load
voltage is larger than the first predetermined value is calculated
from Formula (2) Duty3=1-N.times.Vin/(2.times.Vc) (2) where the
Duty3 is the Duty value, the N is a turn ratio of the second coil
to the first coil, the Vin is an input voltage detected by the
input voltage detecting means, and the Vc is the capacitive load
voltage.
8. The power conversion apparatus according to claim 6, wherein the
Duty value of the third mode when the capacitive load voltage is
larger than the first predetermined value is calculated from
Formula (2) Duty3=1-N.times.Vin/(2.times.Vc) (2) where the Duty3 is
the Duty value, the N is a turn ratio of the second coil to the
first coil, the Vin is an input voltage detected by the input
voltage detecting means, and the Vc is the capacitive load
voltage.
9. The power conversion apparatus according to claim 6, wherein the
first predetermined value calculated from Formula (1) is corrected
using a predetermined correction value.
10. The power conversion apparatus according to claim 7, wherein,
when the Duty value is calculated from Formula (2), the Duty value
is calculated by adding a correction value to the capacitive load
voltage.
11. The power conversion apparatus according to claim 8, wherein,
when the Duty value is calculated from Formula (2), the Duty value
is calculated by adding a correction value to the capacitive load
voltage.
12. The power conversion apparatus according to claim 4, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the Duty value of the first mode is calculated from Formula
(3) Duty1=Imax1.times.L/{Ts(Vin-Vc/N)} (3) where the Duty1 is the
Duty value, the Imax1 is a maximum allowable value of a current
passing through the choke coil, the L is self-inductance of the
choke coil, the Ts is the control cycle, the Vin is an input
voltage detected by the input voltage detecting means, the Vc is
the capacitive load voltage, and the N is a turn ratio of the
second coil to the first coil.
13. The power conversion apparatus according to claim 5, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the first Duty value and the second Duty value of the
second mode are calculated from Formulas (4) and (5)
Duty2l<Imax2.times.L/(Ts.times.Vin) (4)
Duty2h={(Imax2.times.L-Vin.times.Duty2l.times.Ts)/{Ts(Vin-Vc/N)}}+Duty2l
(5) where the Duty2l is either one of the first Duty value and the
second Duty value and the other is the Duty2h, the Duty2h is a
value larger than the Duty2l, the Imax2 is a maximum allowable
value of a current passing through the choke coil, the L is
self-inductance of the choke coil, the Ts is the control cycle, the
Vin is an input voltage detected by the input voltage detecting
means, the Vc is the capacitive load voltage, and the N is a turn
ratio of the second coil to the first coil.
14. The power conversion apparatus according to claim 3, wherein,
under control of the first mode in a first predetermined period,
one of the first and second switching elements is turned OFF, and
the other switching element is alternately turned ON and OFF.
15. The power conversion apparatus according to claim 14, wherein,
under control of the third mode in a second predetermined period,
one of the first and second switching elements is turned ON, and
the other switching element is alternately turned ON and OFF.
16. The power conversion apparatus according to claim 14, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
17. The power conversion apparatus according to claim 1, wherein,
under control of the first mode in a first predetermined period,
one of the first and second switching elements is turned OFF, and
the other switching element is alternately turned ON and OFF.
18. The power conversion apparatus according to claim 17, wherein,
under control of the third mode in a second predetermined period,
one of the first and second switching elements is turned ON, and
the other switching element is alternately turned ON and OFF.
19. The power conversion apparatus according to claim 18, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
20. The power conversion apparatus according to claim 17, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
21. The power conversion apparatus according to claim 1, wherein,
under control of the third mode in a second predetermined period,
one of the first and second switching elements is turned ON, and
the other switching element is alternately turned ON and OFF.
22. The power conversion apparatus according to claim 21, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
23. The power conversion apparatus according to claim 1, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
24. The power conversion apparatus according to claim 1, further
comprising a current detecting means detecting a current value of
the choke coil, wherein, in each of the first and third modes, the
first and second switching elements are controlled in such a way
that the current value detected by the current detecting means
serves as a command current that is a preset value.
25. The power conversion apparatus according to claim 24, wherein
the command current of the third mode is larger than the command
current of the first mode.
26. The power conversion apparatus according to claim 24, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave, and the
addition unit adds the slope signal of a sawtooth wave to the
current value.
27. The power conversion apparatus according to claim 26, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
28. The power conversion apparatus according to claim 24, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
29. The power conversion apparatus according to claim 2, further
comprising a current detecting means detecting a current value in
the choke coil, wherein, in each of the first, second and third
modes, the first and second switching elements are controlled in
such a way that the current value detected by the current detecting
means serves as a command current that is a preset value.
30. The power conversion apparatus according to claim 29, wherein
the command current of the third mode is larger than the command
current of the first mode and larger than the command current of
the second mode.
31. The power conversion apparatus according to claim 29, wherein,
under control of the second mode, an ON-state period of one of the
first and second switching elements is fixed and an ON-state period
of the other of the first and second switching elements is changed
to ensure the current value to serve as the command current.
32. The power conversion apparatus according to claim 31, wherein,
in the second mode, the switching element having a fixed ON-state
period among the first and second switching elements has a Duty
value of not more than 50%.
33. The power conversion apparatus according to claim 29, wherein,
under control of the second mode, the current value at a time point
of turning OFF both of the first and second switching elements is
ensured to serve as the command current.
34. The power conversion apparatus according to claim 33, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
35. The power conversion apparatus according to claim 29, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
36. The power conversion apparatus according to claim 31, wherein,
under control of the second mode, the current value at a time point
of turning OFF both of the first and second switching elements is
ensured to serve as the command current.
37. The power conversion apparatus according to claim 36, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
38. The power conversion apparatus according to claim 36, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
39. The power conversion apparatus according to claim 31, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
40. The power conversion apparatus according to claim 39, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
41. The power conversion apparatus according to claim 31, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
42. The power conversion apparatus according to claim 29, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
43. The power conversion apparatus according to claim 42, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
44. The power conversion apparatus according to claim 32, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
45. The power conversion apparatus according to claim 44, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
46. The power conversion apparatus according to claim 32, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
47. A power conversion apparatus, comprising: a direct current
power supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting one of an ON signal for instructing state transition
to ON, and an OFF signal for instructing state transition to OFF,
to the first and second switching elements, wherein the center tap
is connected to an output terminal of the choke coil and the
predetermined connecting point is connected to a negative terminal
of the direct current power supply, when the capacitive load
voltage is not larger than a first predetermined value or less, a
first mode is defined as a control under which a control of turning
ON one of the first and second switching elements and turning OFF
the other switching element is alternated with a control of turning
OFF both of the first and second switching elements, and when the
capacitive load voltage is larger than the first predetermined
value, a third mode is defined as a control under which a control
of turning ON one of the first and second switching elements and
turning OFF the other switching element is alternated with a
control of turning ON both of the first and second switching
elements.
48. A power conversion apparatus, comprising: a direct current
power supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting one of an ON signal for instructing state transition
to ON, and an OFF signal for instructing state transition to OFF,
to the first and second switching elements, wherein the center tap
is connected to an output terminal of the choke coil and the
predetermined connecting point is connected to a negative terminal
of the direct current power supply, when the capacitive load
voltage is not larger than a second predetermined value that is
smaller than a first predetermined value, a first mode is defined
as a control under which a control of turning ON one of the first
and second switching elements and turning OFF the other switching
element is alternated with a control of turning OFF both of the
first and second switching elements, when the capacitive load
voltage is larger than the second predetermined value but not
larger than the first predetermined value, a second mode is defined
as a control under which a control of turning ON both of the first
and second switching elements, a control of turning ON one of the
first and second switching elements and turning OFF the other
switching element, and a control of turning OFF both of the first
and second switching elements are sequentially repeated, and when
the capacitive load voltage is larger than the first predetermined
value, a third mode is defined as a control under which a control
of turning ON one of the first and second switching elements and
turning OFF the other switching element is alternated with a
control of turning ON both of the first and second switching
elements.
49. The power conversion apparatus according to claim 47, wherein
the pulse generation unit transmits signals having an equal control
cycle to the respective first and second switching elements.
50. A power conversion apparatus, comprising: a direct current
power supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting a first PWM signal and a second PWM signal having an
equal control cycle and serving as driving signals for the
switching elements, the first PWM signal being transmitted to the
first switching element, the second PWM signal being transmitted to
the second switching element, wherein the center tap is connected
to an output terminal of the choke coil and the predetermined
connecting point is connected to a negative terminal of the direct
current power supply, when the capacitive load voltage is not
larger than a first predetermined value, a first mode is defined as
a control under which a phase difference between the first and
second PWM signals corresponds to a half of the control cycle and
Duty values of the first and second PWM signals are an equal in
value and less than 0.5, and when the capacitive load voltage is
larger than the first predetermined value, a third mode is defined
as a control under which a phase difference between the first and
second PWM signals corresponds to a half of the control cycle and
Duty values of the first and second PWM signals are an equal value
larger than 0.5.
51. A power conversion apparatus, comprising: a direct current
power supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting a first PWM signal and a second PWM signal having an
equal control cycle and serving as driving signals for the
switching elements, the first PWM signal being transmitted to the
first switching element, the second PWM signal being transmitted to
the second switching element, wherein the center tap is connected
to an output terminal of the choke coil and the predetermined
connecting point is connected to a negative terminal of the direct
current power supply, when the capacitive load voltage is not
larger than a second predetermined value that is smaller than a
first predetermined value, a first mode is defined as a control
under which a phase difference between the first and second PWM
signals corresponds to a half of the control cycle and Duty values
of the first and second PWM signals are an equal in value and less
than 0.5, when the capacitive load voltage is larger than the
second predetermined value but not larger than the first
predetermined value, a second mode is defined as a control under
which a phase difference between the first and second PWM signals
corresponds to one control cycle, the first and second PWM signals
are signals where a signal of a first Duty value is alternated with
a signal of a second Duty value different from the first Duty value
on a control-cycle basis, a result of adding the first Duty value
and the second Duty value is less than 1, and a time point of
switching the signal of the first Duty value from OFF to ON and a
time point of switching the signal of the second Duty value from
OFF to ON have a difference corresponding to one cycle of the
control cycle, and when the capacitive load voltage is larger than
the first predetermined value, a third mode is defined as a control
under which a phase difference between the first and second PWM
signals corresponds to a half of the control cycle and Duty values
of the first and second PWM signals are an equal in value and more
than 0.5.
52. The power conversion apparatus according to claim 50, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the first predetermined value is calculated from Formula
(1) V1=N.times.Vin/(2.times.(1-Duty0)) (1), where the V1 is the
first predetermined value, the N is a turn ratio of the second coil
to the first coil, the Vin is an input voltage detected by the
input voltage detecting means, and the Duty0 is an initial value of
the Duty value in starting control of the third mode, the initial
value being more than 0.5 but less than 1.
53. The power conversion apparatus according to claim 50, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the Duty value of the third mode when the capacitive load
voltage is larger than the first predetermined value is calculated
from Formula (2) Duty3=1-N.times.Vin/(2.times.Vc) (2) where the
Duty3 is the Duty value, the N is a turn ratio of the second coil
to the first coil, the Vin is an input voltage detected by the
input voltage detecting means, and the Vc is the capacitive load
voltage.
54. The power conversion apparatus according to claim 52, wherein
the Duty value of the third mode when the capacitive load voltage
is larger than the first predetermined value is calculated from
Formula (2) Duty3=1-N.times.Vin/(2.times.Vc) (2) where the Duty3 is
the Duty value, the N is a turn ratio of the second coil to the
first coil, the Vin is an input voltage detected by the input
voltage detecting means, and the Vc is the capacitive load
voltage.
55. The power conversion apparatus according to claim 52, wherein
the first predetermined value calculated from Formula (1) is
corrected using a predetermined correction value.
56. The power conversion apparatus according to claim 53, wherein,
in calculating the Duty value from Formula (2), a correction value
is added to the capacitive load voltage.
57. The power conversion apparatus according to claim 54, wherein,
in calculating the Duty value from Formula (2), a correction value
is added to the capacitive load voltage.
58. The power conversion apparatus according to claim 50, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the Duty value of the first mode is calculated from Formula
(3) Duty1=Imax1.times.L/{Ts(Vin-Vc/N)} (3) where the Duty1 is the
Duty value, the Imax1 is a maximum allowable value of a current
passing through the choke coil, the L is self-inductance of the
choke coil, the Ts is the control cycle, the Vin is an input
voltage detected by the input voltage detecting means, the Vc is
the capacitive load voltage, and the N is a turn ratio of the
second coil to the first coil.
59. The power conversion apparatus according to claim 51, further
comprising an input voltage detecting means detecting an input
voltage that is a voltage of the direct current power supply,
wherein the first Duty value and the second Duty value of the
second mode are calculated from Formulas (4) and (5)
Duty2l<Imax2.times.L/(Ts.times.Vin) (4)
Duty2h={(Imax2.times.L-Vin.times.Duty2l.times.Ts)/{Ts(Vin-Vc/N)}}+Duty2l
(5) where the Duty2l is either one of the first Duty value and the
second Duty value, and the other Duty value is the Duty2h, the
Duty2h is more than the Duty2l, the Imax2 is a maximum allowable
value of a current passing through the choke coil, the L is
self-inductance of the choke coil, the Ts is the control cycle, the
Vin is an input voltage detected by the input voltage detecting
means, the Vc is the capacitive load voltage, and the N is a turn
ratio of the second coil to the first coil.
60. The power conversion apparatus according to claim 49, wherein,
under control of the first mode in a first predetermined period,
one of the first and second switching elements is turned OFF, and
the other switching element is alternately turned ON and OFF.
61. The power conversion apparatus according to claim 60, wherein,
under control of the third mode in a second predetermined period,
one of the first and second switching elements is turned ON, and
the other switching element is alternately turned ON and OFF.
62. The power conversion apparatus according to claim 60, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
63. The power conversion apparatus according to claim 47, wherein,
under control of the first mode in a first predetermined period,
one of the first and second switching elements is turned OFF, and
the other switching element is alternately turned ON and OFF.
64. The power conversion apparatus according to claim 63, wherein,
under control of the third mode in a second predetermined period,
one of the first and second switching elements is turned ON, and
the other switching element is alternately turned ON and OFF.
65. The power conversion apparatus according to claim 64, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
66. The power conversion apparatus according to claim 63, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
67. The power conversion apparatus according to claim 47, wherein,
under control of the third mode in a second predetermined period,
one of the first and second switching elements is turned ON, and
the other switching element is alternately turned ON and OFF.
68. The power conversion apparatus according to claim 67, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
69. The power conversion apparatus according to claim 47, wherein,
in a third predetermined period, an accumulated value of time in an
ON-state of the first switching element is equal to an accumulated
value of time in an ON-state of the second switching element.
70. The power conversion apparatus according to claim 47, further
comprising a current detecting means detecting a current value of
the choke coil, wherein, in each of the first and third modes, the
first and second switching elements are controlled in such a way
that the current value detected by the current detecting means
serves as a command current that is a preset value.
71. The power conversion apparatus according to claim 70, wherein
the command current of the third mode is larger than the command
current of the first mode.
72. The power conversion apparatus according to claim 70, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave, and the
addition unit adds the slope signal of a sawtooth wave to the
current value.
73. The power conversion apparatus according to claim 72, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
74. The power conversion apparatus according to claim 70, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
75. The power conversion apparatus according to claim 48, further
comprising a current detecting means detecting a current value in
the choke coil, wherein, in each of the first, second and third
modes, the first and second switching elements are controlled in
such a way that the current value detected by the current detecting
means serves as a command current that is a preset value.
76. The power conversion apparatus according to claim 75, wherein
the command current of the third mode is larger than the command
current of the first mode and larger than the command current of
the second mode.
77. The power conversion apparatus according to claim 75, wherein,
under control of the second mode, an ON-state period of one of the
first and second switching elements is fixed and an ON-state period
of the other of the first and second switching elements is changed
to ensure the current value to serve as the command current.
78. The power conversion apparatus according to claim 77, wherein,
in the second mode, the switching element having a fixed ON-state
period among the first and second switching elements has a Duty
value of not more than 50%.
79. The power conversion apparatus according to claim 75, wherein,
under control of the second mode, the current value at a time point
of turning OFF both of the first and second switching elements is
ensured to serve as the command current.
80. The power conversion apparatus according to claim 79, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
81. The power conversion apparatus according to claim 75, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
82. The power conversion apparatus according to claim 77, wherein,
under control of the second mode, the current value at a time point
of turning OFF both of the first and second switching elements is
ensured to serve as the command current.
83. The power conversion apparatus according to claim 82, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
84. The power conversion apparatus according to claim 82, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
85. The power conversion apparatus according to claim 77, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
86. The power conversion apparatus according to claim 85, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
87. The power conversion apparatus according to claim 77, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
88. The power conversion apparatus according to claim 75, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
89. The power conversion apparatus according to claim 88, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
90. The power conversion apparatus according to claim 78, further
comprising: a slope compensation unit generating a slope signal;
and an addition unit adding the slope signal to the current value,
wherein, in the first mode and a second mode, the slope
compensation unit generates the slope signal having a zero value
and the addition unit adds the slope signal having a zero value to
the current value, and in the third mode, the slope compensation
unit generates the slope signal of a sawtooth wave and the addition
unit adds the slope signal of a sawtooth wave to the current
value.
91. The power conversion apparatus according to claim 90, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
92. The power conversion apparatus according to claim 78, wherein,
in each of the first, second and third modes, peak current control
is performed in such a way that the current value serves as the
command current.
93. A method for controlling a power conversion apparatus, the
power conversion apparatus including: a direct current power
supply; a choke coil having an input terminal connected to a
positive terminal of the direct current power supply; a first coil
having a center tap, with both ends connected to a predetermined
connecting point, one end via a first switching element and the
other end via a second switching element; a second coil
magnetically coupled to the first coil; a capacitive load connected
to the second coil via a rectifying circuit; a capacitive load
voltage detecting means detecting a capacitive load voltage as a
voltage of the capacitive load; and a pulse generation unit
transmitting one of an ON signal for instructing state transition
to ON, and an OFF signal for instructing state transition to OFF,
to the first and second switching elements, wherein the center tap
is connected to a negative terminal of the direct current power
supply and the predetermined connecting point is connected to an
output terminal of the choke coil, the method comprising: a step of
control in a first mode under which, when the capacitive load
voltage is not larger than a first predetermined value, a control
of turning ON one of the first and second switching elements and
turning OFF the other switching element is alternated with a
control of turning OFF both of the first and second switching
elements; and a step of control in a third mode under which, when
the capacitive load voltage is larger than the first predetermined
value, a control of turning ON one of the first and second
switching elements and turning OFF the other switching element is
alternated with a control of turning ON both of the first and
second switching elements.
94. A method for controlling a power conversion apparatus, the
power conversion apparatus including a direct current power supply;
a choke coil having an input terminal connected to a positive
terminal of the direct current power supply; a first coil having a
center tap, with both ends connected to a predetermined connecting
point, one end via a first switching element and the other end via
a second switching element; a second coil magnetically coupled to
the first coil; a capacitive load connected to the second coil via
a rectifying circuit; a capacitive load voltage detecting means
detecting a capacitive load voltage as a voltage of the capacitive
load; and a pulse generation unit transmitting one of an ON signal
for instructing state transition to ON, and an OFF signal for
instructing state transition to OFF, to the first and second
switching elements, wherein the center tap is connected to a
negative terminal of the direct current power supply and the
predetermined connecting point is connected to an output terminal
of the choke coil, the method comprising: a step of control in a
first mode under which, when the capacitive load voltage is not
larger than a second predetermined value that is smaller than a
first predetermined value, a control of turning ON one of the first
and second switching elements and turning OFF the other switching
element is alternated with a control of turning OFF both of the
first and second switching elements, a step of control in a second
mode under which, when the capacitive load voltage is larger than
the second predetermined value but not larger than the first
predetermined value, a control of turning ON both of the first and
second switching elements, a control of turning ON one of the first
and second switching elements and turning OFF the other switching
element, and a control of turning OFF both of the first and second
switching elements are sequentially repeated; and a step of control
in a third mode under which, when the capacitive load voltage is
larger than the first predetermined value, a control of turning ON
one of the first and second switching elements and turning OFF the
other switching element is alternated with a control of turning ON
both of the first and second switching elements.
95. A method for controlling a power conversion apparatus, the
power conversion apparatus including a direct current power supply;
a choke coil having an input terminal connected to a positive
terminal of the direct current power supply; a first coil having a
center tap, with both ends connected to a predetermined connecting
point, one end via a first switching element and the other end via
a second switching element; a second coil magnetically coupled to
the first coil; a capacitive load connected to the second coil via
a rectifying circuit; a capacitive load voltage detecting means
detecting a capacitive load voltage as a voltage of the capacitive
load; and a pulse generation unit transmitting a first PWM signal
and a second PWM signal having an equal control cycle and serving
as driving signals for the switching elements, the first PWM signal
being transmitted to the first switching element, the second PWM
signal being transmitted to the second switching element, wherein
the center tap is connected to a negative terminal of the direct
current power supply and the predetermined connecting point is
connected to an output terminal of the choke coil, the method
comprising: a step of control in a first mode under which, when the
capacitive load voltage is not larger than a first predetermined
value, a phase difference between the first and second PWM signals
corresponds to a half of the control cycle and Duty values of the
first and second PWM signals are an equal in value and less than
0.5; and a step of control in a third mode under which, when the
capacitive load voltage is larger than the first predetermined
value, a phase difference between the first and second PWM signals
corresponds to a half of the control cycle and Duty values of the
first and second PWM signals are an equal in value and more than
0.5.
96. A method for controlling a power conversion apparatus, the
power conversion apparatus including a direct current power supply;
a choke coil having an input terminal connected to a positive
terminal of the direct current power supply; a first coil having a
center tap, with both ends connected to a predetermined connecting
point, one end via a first switching element and the other end via
a second switching element; a second coil magnetically coupled to
the first coil; a capacitive load connected to the second coil via
a rectifying circuit; a capacitive load voltage detecting means
detecting a capacitive load voltage as a voltage of the capacitive
load; and a pulse generation unit transmitting a first PWM signal
and a second PWM signal having an equal control cycle and serving
as driving signals for the switching elements, the first PWM signal
being transmitted to the first switching element, the second PWM
signal being transmitted to the second switching element, wherein
the center tap is connected to a negative terminal of the direct
current power supply and the predetermined connecting point is
connected to an output terminal of the choke coil, the method
comprising: a step of control in a first mode under which, when the
capacitive load voltage is not larger than a second predetermined
value that is smaller than a first predetermined value, a phase
difference between the first and second PWM signals corresponds to
a half of the control cycle and Duty values of the first and second
PWM signals are an equal in value and less than 0.5, a step of
control in a second mode under which, when the capacitive load
voltage is larger than the second predetermined value but not
larger than the first predetermined value, a phase difference
between the first and second PWM signals corresponds to one control
cycle, the first and second PWM signals are signals where a signal
of a first Duty value is alternated with a signal of a second Duty
value different from the first Duty value on a control-cycle basis,
a result of adding the first Duty value and the second Duty value
is less than 1, and a time point of switching the signal of the
first Duty value from OFF to ON and a time point of switching the
signal of the second Duty value from OFF to ON have a difference
corresponding to one control cycle; and a step of control in a
third mode under which, when the capacitive load voltage is larger
than the first predetermined value, a phase difference between the
first and second PWM signals corresponds to a half of the control
cycle and Duty values of the first and second PWM signals are an
equal in value and more than 0.5.
Description
BACKGROUND
[0001] Technical Field
[0002] The present disclosure relates to a power conversion
technique for charging a capacitive load.
[0003] Background Art
[0004] PTL 1 describes a power supply control apparatus that
charges a capacitive load using a direct current power supply. The
power supply control apparatus described in PTL 1 is provided with
a main storage device, a capacitive load connected between power
lines of the main storage device, and an auxiliary storage device
disposed between the power lines of the main storage device and
connected parallel to the capacitive load via a bidirectional
converter. Power supply/reception between the main storage device
and the auxiliary storage device is performed using the
bidirectional converter. The power supply control apparatus
described in PTL 1 supplies power of the auxiliary storage device
to the capacitive load using the bidirectional converter, thereby
charging the capacitive load until the voltage thereof becomes
equal to the voltage of the main storage device.
CITATION LIST
Patent Literature
[0005] PTL 1: JP-A-2007-295699
[0006] In the power supply control apparatus described in PTL 1,
when the bidirectional converter is a current input push-pull DCDC
converter provided with a choke coil on the auxiliary battery side,
the capacitive load is charged by repeatedly increasing and
decreasing the current passing through the choke coil. Taking
account of reducing cost and size of the system, the power supply
control apparatus described in PTL 1 is not provided with a
limiting resistor or the like to prevent inrush current.
[0007] A necessary condition for decreasing the current passing
through the choke coil is that the value of the voltage of the
auxiliary battery is smaller than a value obtained by dividing the
voltage of the capacitive load by a turn ratio of the coils
constituting the bidirectional converter. Accordingly, when the
voltage of the capacitive load is small, such as when charging is
started, the current passing through the choke coil continues
increasing, which may lead to degradation or breakage of the DCDC
converter.
SUMMARY
[0008] The present disclosure has been made to provide a power
conversion technique with which excessive current in a circuit is
minimized, while a capacitive load is promptly charged.
[0009] A power conversion apparatus of the present disclosure
includes: a direct current power supply; and a choke coil having an
input terminal connected to a positive terminal of the direct
current power supply. In addition, the power conversion apparatus
includes: a first coil having a center tap, with both ends
connected to a predetermined connecting point, one end via a first
switching element and the other end via a second switching element;
a second coil magnetically coupled to the first coil; and a
capacitive load connected to the second coil via a rectifying
circuit. In addition, the power conversion apparatus includes: a
capacitive load voltage detecting means detecting a capacitive load
voltage that is a voltage of the capacitive load; and a pulse
generation unit transmitting a first PWM signal and a second PWM
signal having an equal control cycle and serving as driving signals
for the switching elements, the first PWM signal being transmitted
to the first switching element, the second PWM signal being
transmitted to the second switching element. In the power
conversion apparatus of the present disclosure, the center tap is
connected to a negative terminal of the power supply and the
predetermined connecting point is connected to an output terminal
of the choke coil. Alternatively, in the power conversion
apparatus, the center tap is connected to an output terminal of the
choke coil and the predetermined connecting point is connected to a
negative terminal of the power supply. In the power conversion
apparatus, when the capacitive load voltage is not larger than a
first predetermined value, the following control is defined as a
first mode. A phase difference between the first and second PWM
signals corresponds to a half of the control cycle, and Duty values
of the first and second PWM signals are an equal in value and less
than 0.5. When the capacitive load voltage is larger than the first
predetermined value, the following control is defined as a third
mode. A phase difference between the first and second PWM signals
corresponds to a half of the control cycle and Duty values of the
first and second PWM signals are an equal in value and more than
0.5.
[0010] The power conversion apparatus of the present disclosure
includes: a direct current power supply; and a choke coil having an
input terminal connected to a positive terminal of the direct
current power supply. In addition, the power conversion apparatus
includes:
[0011] a first coil having a center tap, with both ends connected
to a predetermined connecting point, one end via a first switching
element and the other end via a second switching element; a second
coil magnetically coupled to the first coil; and a capacitive load
connected to the second coil via a rectifying circuit. In addition,
the power conversion apparatus includes: a capacitive load voltage
detecting means detecting a capacitive load voltage that is a
voltage of the capacitive load; and a pulse generation unit
transmitting one of an ON signal for instructing state transition
to ON, and an OFF signal for instructing state transition to OFF,
to the first and second switching elements. In the power conversion
apparatus of the present disclosure, the center tap is connected to
a negative terminal of the direct current power supply and the
predetermined connecting point is connected to an output terminal
of the choke coil. Alternatively, in the power conversion
apparatus, the center tap is connected to an output terminal of the
choke coil and the predetermined connecting point is connected to a
negative terminal of the direct current power supply. In the power
conversion apparatus, when the capacitive load voltage is not
larger than a first predetermined value, the following control is
defined as a first mode. In the first mode, a control of turning ON
one of the first and second switching elements and turning OFF the
other switching element is alternated with a control of turning OFF
both of the first and second switching elements. In the power
conversion apparatus, when the capacitive load voltage is larger
than the first predetermined value, the following control is
defined as a third mode. In the third mode, a control of turning ON
one of the first and second switching elements and turning OFF the
other switching element is alternated with a control of turning ON
both of the first and second switching elements.
[0012] In a current input push-pull DCDC converter having a choke
coil on the power supply side relative to a transformer, when both
the first and second switching elements are in an ON-state, the
first coil is in a short-circuited state. Therefore, the voltage of
the first coil is zero. Accordingly, the input voltage that is the
voltage of the direct current power supply is applied, as it is, to
the choke coil, thereby increasing current in a linear manner.
[0013] When either one of the first and second switching elements
is in an ON-state, increase or decrease of current passing through
the choke coil depends on the input voltage, the capacitive load
voltage that is the voltage of the capacitive load, and a turn
ratio of the coils. That is, when the value of the input voltage is
larger than a value obtained by dividing the capacitive load
voltage by the turn ratio, the voltage applied to the choke coil
has a positive value and the current passing through the choke coil
increases. In contrast, when the value of the input voltage is
smaller than a value obtained by dividing the capacitive load
voltage by the turn ratio, the voltage applied to the choke coil
has a negative value and the current passing through the choke coil
decreases.
[0014] Further, when both the first and second switching elements
are in an OFF-state, the current passing through the choke coil
decreases.
[0015] When the capacitive load voltage is low, such as when charge
of the capacitive load is started, the value of the input voltage
will be smaller than the value obtained by dividing the capacitive
load voltage by the turn ratio. Therefore, if either one of the
first and second switching elements is turned ON, the current
passing through the choke coil keeps increasing. Accordingly, when
the capacitive load voltage is not larger than a first
predetermined value, a control is performed using the first mode,
under which a phase difference between the first and second PWM
signals corresponds to a half of the control cycle, while Duty
values of the first and second PWM signals are an equal in value
and less than 0.5.
[0016] Alternatively, when the capacitive load voltage is not
larger than the first predetermined value, a control is performed
using the first mode, under which a control of turning ON one of
the first and second switching elements and turning OFF the other
switching element is alternated with a control of turning OFF both
of the first and second switching elements.
[0017] In the power conversion apparatus of the present disclosure,
under the control of the first mode, a state where one of the first
and second switching elements is turned ON is alternated with a
state where both of the first and second switching elements are
turned OFF. Accordingly, in the power conversion apparatus of the
present disclosure, there is provided a period in which both of the
first and second switching elements are in an OFF-state to thereby
decrease the current passing through the choke coil in this period.
Thus, the power conversion apparatus of the present disclosure is
able to prevent current accumulated in the choke coil from keeping
increasing. As a result, degradation or failure of the DCDC
converter is minimized.
[0018] In contrast, when the capacitive load voltage is large, such
as when charge of the capacitive load progresses, the value of the
input voltage will be smaller than a value obtained by dividing the
capacitive load voltage by a turn ratio. Therefore, when either one
of the first and second switching elements is turned ON, the
current passing through the choke coil will decrease. To cope with
this, when the capacitive load voltage is larger than the first
predetermined value, a control is performed using the third mode,
under which a phase difference between the first and second PWM
signals is a half of the control cycle, and Duty values of the
first and second PWM signals are ensured to be an equal in value
and more than 0.5.
[0019] Alternatively, when the capacitive load voltage is larger
than the first predetermined value, a control is performed using
the third mode, under which a control of turning ON one of the
first and second switching elements and turning OFF the other
switching element is alternated with a control of turning ON both
of the first and second switching elements.
[0020] In the power conversion apparatus of the present disclosure,
under the control of the third mode, a state where both of the
first and second switching elements are turned ON is alternated
with a state where one of the first and second switching elements
is turned ON. Accordingly, the power conversion apparatus of the
present disclosure can increase a current passing through the choke
coil in a period in which both of the first and second switching
elements are in an ON-state. In the power conversion apparatus of
the present disclosure, the current passing through the choke coil
is decreased in a period in which either one of the first and
second switching elements is turned ON. Thus, rapid charge is
conducted for a capacitive load in which charge is progressing.
[0021] A power conversion apparatus of the present disclosure
includes: a direct current power supply; and a choke coil having an
input terminal connected to a positive terminal of the direct
current power supply. In addition, the power conversion apparatus
includes: a first coil having a center tap, with both ends
connected to a predetermined connecting point, one end via a first
switching element and the other end via a second switching element;
a second coil magnetically coupled to the first coil; and a
capacitive load connected to the second coil via a rectifying
circuit. In addition, the power conversion apparatus includes: a
capacitive load voltage detecting means detecting a capacitive load
voltage that is a voltage of the capacitive load; and a pulse
generation unit transmitting a first PWM signal and a second PWM
signal having an equal control cycle and serving as driving signals
for the switching elements, the first PWM signal being transmitted
to the first switching element, the second PWM signal being
transmitted to the second switching element. In the power
conversion apparatus of the present disclosure, the center tap is
connected to a negative terminal of the power supply and the
predetermined connecting point is connected to an output terminal
of the choke coil. Alternatively, in the power conversion
apparatus, the center tap is connected to an output terminal of the
choke coil and the predetermined connecting point is connected to a
negative terminal of the power supply. In the power conversion
apparatus, when the capacitive load voltage is not larger than a
second predetermined value that is smaller than a first
predetermined value, the following control is defined as a first
mode. A phase difference between the first and second PWM signals
corresponds to a half of the control cycle, and Duty values of the
first and second PWM signals are an equal in value and less than
0.5. In the power conversion apparatus, when the capacitive load
voltage is larger than the second predetermined value but not
larger than the first predetermined value, the following control is
defined as a second mode. A phase difference between the first and
second PWM signals corresponds to one control cycle, the first and
second PWM signals are signals where a signal of a first Duty value
is alternated with a signal of a second Duty value different from
the first Duty value on a control-cycle basis, and a result of
adding the first Duty value and the second Duty value is less than
1. Further, a time point of switching the signal of the first Duty
value from OFF to ON, and a time point of switching the signal of
the second Duty value from OFF to ON have a difference
corresponding to one control cycle. In the power conversion
apparatus, when the capacitive load voltage is larger than the
first predetermined value, the following control is defined as a
third mode. A phase difference between the first and second PWM
signals corresponds to a half of the control cycle, and Duty values
of the first and second PWM signals are an equal in value and more
than 0.5.
[0022] The power conversion apparatus of the present disclosure
includes: a direct current power supply; and a choke coil having an
input terminal connected to a positive terminal of the direct
current power supply. In addition, the power conversion apparatus
includes: a first coil having a center tap, with both ends
connected to a predetermined connecting point, one end via a first
switching element and the other end via a second switching element;
a second coil magnetically coupled to the first coil; and a
capacitive load connected to the second coil via a rectifying
circuit. In addition, the power conversion apparatus includes: a
capacitive load voltage detecting means detecting a capacitive load
voltage that is a voltage of the capacitive load; and a pulse
generation unit transmitting one of an ON signal for instructing
state transition to ON, and an OFF signal for instructing state
transition to OFF, to the first and second switching elements. In
the power conversion apparatus of the present disclosure, the
center tap is connected to a negative terminal of the direct
current power supply and the predetermined connecting point is
connected to an output terminal of the choke coil. Alternatively,
in the power conversion apparatus, the center tap is connected to
an output terminal of the choke coil and the predetermined
connecting point is connected to a negative terminal of the direct
current power supply. In the power conversion apparatus, when the
capacitive load voltage is not larger than a second predetermined
value that is smaller than a first predetermined value, the
following control is defined as a first mode. In the first mode, a
control of turning ON one of the first and second switching
elements and turning OFF the other switching element is alternated
with a control of turning OFF both of the first and second
switching elements. In the power conversion apparatus, when the
capacitive load voltage is larger than the second predetermined
value but not larger than the first predetermined value, the
following control is defined as a second mode. In the second mode,
a control of turning ON both of the first and second switching
elements, a control of turning ON one of the first and second
switching elements and turning OFF the other switching element, and
a control of turning OFF both of the first and second switching
elements are sequentially repeated. In the power conversion
apparatus, when the capacitive load voltage is larger than the
first predetermined value, the following control is defined as a
third mode. In the third mode, a control of turning ON one of the
first and second switching elements and turning OFF the other
switching element is alternated with a control of turning ON both
of the first and second switching elements.
[0023] When the capacitive load voltage is not larger than a first
predetermined value, charge under the control of the first mode
increases the capacitive load voltage. When the value obtained by
dividing the capacitive load voltage by the turn ratio of the coils
is larger than the value of the input voltage, the increase in the
current passing through the choke coil will be lowered to thereby
lower the charging rate, if the current passing through the choke
coil does not increase and the value obtained by dividing the
capacitive load voltage by the turn ratio of the coils is smaller
than the value of the input voltage.
[0024] To cope with this, when the value obtained by dividing the
capacitive load voltage by the turn ratio of the coils is larger
than the value of the input voltage, a second predetermined value
that is smaller than the first predetermined value is set as a
threshold of the capacitive load voltage. Then, when the capacitive
load voltage is larger than the second predetermined value but not
larger than a first predetermined value, the following control is
performed. Firstly, a phase difference between the first and second
PWM signals corresponds to one control cycle. Further, in a first
PWM signal and a second PWM signal, a signal of a first Duty value
is alternated with a signal of a second Duty value different from
the first Duty value on a control-cycle basis. Further, a result of
adding the first Duty value and the second Duty value is less than
1, and a time point of switching the signal of the first Duty value
from OFF to ON, and a time point of switching the signal of the
second Duty value from OFF to ON have a difference corresponding to
one control cycle, and thus the control of the second mode is
performed.
[0025] Alternatively, a control is performed using the second mode,
under which, when the capacitive load voltage is larger than the
second predetermined value but not larger than the first
predetermined value, a control of turning ON both of the first and
second switching elements, a control of turning ON one of the first
and second switching elements and turning OFF the other switching
element, and a control of turning OFF both of the first and second
switching elements are sequentially repeated.
[0026] In the power conversion apparatus of the present disclosure,
the control of the second mode can provide a period in which both
of the first and second switching elements are turned ON, a period
in which either one of the first and second switching elements is
in turned ON, and a period in which both of the first and second
switching elements are turned OFF.
[0027] That is, in the power conversion apparatus of the present
disclosure, firstly, the first and second switching elements are
concurrently turned ON to increase the current passing through the
choke coil. Then, the ON-state of either one of the first and
second switching elements is kept, and the other switching element
is turned OFF. With this configuration, when the value of the input
voltage is larger than a value obtained by dividing the capacitive
load voltage by the turn ratio, the current passing through the
choke coil will increase. In contrast, when the value of the input
voltage is smaller than the value obtained by dividing the
capacitive load voltage by the turn ratio, the current passing
through the choke coil will decrease. Charge of the capacitive load
is carried out in this period. After that, in the power conversion
apparatus of the present disclosure, both of the first and second
switching elements are turned OFF to decrease the current passing
through the choke coil.
[0028] Accordingly, in the power conversion apparatus of the
present disclosure, when charge of the capacitive load progresses
and the capacitive load voltage has become equal to or larger than
the second predetermined value, the current passing through the
choke coil can be increased and thus the charging rate of the
capacitive load can be improved. In the power conversion apparatus
of the present disclosure, a period in which both of the first and
second switching elements are turned OFF is provided in the second
mode as well. As a result the current passing through the choke
coil is prevented from being kept increasing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In the accompanying drawings:
[0030] FIG. 1 is a circuit diagram illustrating a power conversion
apparatus, according to a first embodiment;
[0031] FIG. 2A is a diagram illustrating a current passing through
the power conversion apparatus when both of a first switching
element and a second switching element are turned ON, and FIG. 2B
is a diagram illustrating the equivalent circuit;
[0032] FIG. 3A is a diagram illustrating a passing through the
power conversion apparatus when the first switching element is
turned ON and the second switching element is turned OFF, and FIG.
3B is a diagram illustrating the equivalent circuit;
[0033] FIG. 4 is a flow chart illustrating a series of processing
steps, according to the first embodiment;
[0034] FIG. 5 shows diagrams illustrating PWM signals, where FIG.
5A is a diagram illustrating PWM signals in a first mode, FIG. 5B
is a diagram illustrating PWM signals in a second mode, and FIG. 5C
is a diagram illustrating PWM signals in a third mode;
[0035] FIG. 6 is a circuit diagram illustrating a power conversion
apparatus, according to a third embodiment;
[0036] FIG. 7 is a diagram illustrating a relationship between a
first maximum allowable value and a Duty value in a first mode,
according to a fourth embodiment;
[0037] FIG. 8 is a diagram illustrating a second maximum allowable
value and a Duty value in a second mode, according to the fourth
embodiment;
[0038] FIG. 9 shows diagrams illustrating control signals,
according to a fifth embodiment, where FIG. 9A is a diagram
illustrating control signals in a first mode, FIG. 9B is a diagram
illustrating control signals in a second mode, and FIG. 9C is a
diagram illustrating control signals in a third mode;
[0039] FIG. 10 shows diagrams illustrating control signals,
according to a sixth embodiment, where FIG. 10A is a diagram
illustrating control signals in a first mode, FIG. 10B is a diagram
illustrating control signals in a second mode, and FIG. 10C is a
diagram illustrating control signals in a third mode;
[0040] FIG. 11 is a circuit diagram of a power conversion
apparatus, according to a seventh embodiment;
[0041] FIG. 12 is a block diagram illustrating processes performed
by a pulse generation unit in the power conversion apparatus,
according to the seventh embodiment; and
[0042] FIG. 13 shows diagrams each illustrating a reactor current
in a second mode, according to the seventh embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] With reference to the drawings, some embodiments will be
described. In the embodiments described below, the parts identical
with or equivalent to each other are given the same reference signs
in the drawings and the same description is applied to the parts of
identical reference signs.
First Embodiment
[0044] A power conversion apparatus according to the present
embodiment is installed in a hybrid vehicle provided with a
secondary battery, such as a lead battery with a nominal voltage of
12 V, and a high voltage battery, such as a lithium ion battery
with a nominal voltage of several hundred V.
[0045] FIG. 1 shows a circuit diagram of a power conversion
apparatus according to the present embodiment. A power conversion
apparatus 1 according to the present embodiment includes a DCDC
converter 10 and a secondary battery 20, which is a direct current
power supply connected to input terminals of the DCDC converter 10.
The power conversion apparatus 1 also includes a capacitive load 30
(smoothing capacitor) connected in parallel to output terminals of
the DCDC converter 10, and connecting terminals 40a and 40b
provided to the output terminals of the DCDC converter 10. Power
accumulated in the secondary battery 20 is transformed by the DCDC
converter 10 and outputted from the connecting terminals 40a and
40b. Power inputted from the connecting terminals 40a and 40b is
transformed by the DCDC converter 10 and inputted to the secondary
battery 20. To the connecting terminals 40a and 40b, a high voltage
battery, an electrical load, a generator, and the like are
connected, which are able to supply/receive power to/from the
secondary battery 20.
[0046] The DCDC converter 10 is provided with a choke coil 11, a
transformer Tr, a bridge circuit 14, a first switching element Q1,
and a second switching element Q2.
[0047] The transformer Tr is composed of a first coil L1 and a
second coil L2 that are magnetically coupled to each other, with
the first coil L1 being provided with a center tap 13. The number
of turns of the second coil L2 is N/2 times of the number of turns
of the first coil L1. That is, the number of turns of the second
coil L2 is N times of the number of turns of the first coil L1
covering from either one end thereof to the center tap 13. The
second coil L2 is connected to the capacitive load 30 via the
bridge circuit 14 and the output terminals of the DCDC converter
10.
[0048] The bridge circuit 14 is provided with a switching element
and a diode to function as a rectifying circuit in supplying power
from the first coil L1 side to the second coil L2 side and function
as a switching circuit in supplying power from the second coil L2
side to the first coil L1 side.
[0049] The first switching element Q1 and the second switching
element Q2 are MOSFETs. Of both ends of the first coil L1, one end
is connected to a source of the first switching element Q1 and the
other end is connected to a source of the second switching element
Q2. On the other hand, both a drain of the first switching element
Q1 and a drain of the second switching element Q2 are connected to
a predetermined connecting point 12. To the predetermined
connecting point 12, an output terminal of the choke coil 11 is
connected, and an input terminal of the choke coil 11 is connected
to a positive terminal of the secondary battery 20 via an input
terminal of the DCDC converter 10. The center tap 13 of the first
coil L1 is connected to a negative terminal of the secondary
battery 20 via an input terminal of the DCDC converter 10. The
first switching element Q1 and the second switching element Q2 have
a first parasitic diode D1 and a second parasitic diode D2,
respectively, which are in reverse parallel connection.
[0050] The DCDC converter 10 is provided with an input voltage
detecting means 15, a capacitive load voltage detecting means 16, a
pulse generation unit 17, and a driving circuit 18. The input
voltage detecting means 15 detects an input voltage Vin inputted
from the secondary battery 20 to the choke coil 11. The capacitive
load voltage detecting means 16 detects a capacitive load voltage
Vc of the capacitive load 30.
[0051] The input voltage Vin detected by the input voltage
detecting means 15 and the capacitive load voltage Vc detected by
the capacitive load voltage detecting means 16 are inputted to the
pulse generation unit 17. The pulse generation unit 17 generates a
first PWM signal which is a driving signal of the first switching
element Q1, and a second PWM signal which is a driving signal of
the second switching element Q2, on the basis of the inputted input
voltage Vin and capacitive load voltage Vc, and transmits the
generated PWM signals to the driving circuit 18. The driving signal
herein refers to a signal instructing the first switching element
Q1 or the second switching element Q2 state transition to either
one of an ON state and an OFF state. The signal instructing state
transition to ON (ON driving) is an ON signal, and the signal
instructing state transition to OFF (OFF driving) is an OFF
signal.
[0052] The driving circuit 18 drives the first switching element Q1
on the basis of the first PWM signal received from the pulse
generation unit 17 and drives the second switching element Q2 on
the basis of the second PWM signal.
[0053] In the present embodiment, the capacitive load 30 is charged
by the power accumulated in the secondary battery 20. In this case,
the DCDC converter 10 functions as a current input push-pull DCDC
converter. When power supply of the vehicle is turned ON, a charge
start command is generated in an ECU installed in the vehicle to
start charge. On the other hand, charge is carried out using, as a
target voltage, a voltage that is approximate to the voltage of the
high voltage battery, until the capacitive load voltage Vc reaches
the target voltage. As a value of the target voltage, a value
memorized in a memory of the ECU may be used, or the value may be
calculated on the basis of a measurement value of the voltage of
the high voltage battery. As a method of acquiring the charge start
command and the value of the target voltage, a means for acquiring
them from outside the vehicle may be used.
[0054] FIG. 2A shows a path of current passing through the circuit
when both of the first and second switching elements Q1 and Q2 are
turned ON in the present embodiment. FIG. 2B shows an equivalent
circuit when both of the first and second switching elements Q1 and
Q2 are turned ON in the present embodiment. In this state, since
the first coil L1 is in a short-circuited state, the voltage of the
first coil L1 is zero. Accordingly, the input voltage Vin is
applied to the choke Coil 11.
[0055] An increase .DELTA.I per unit time [A/s] of the current
passing through the choke coil 11 is expressed by the following
equation (1), where L[H] is a self-inductance of the choke coil
11.
.DELTA.I=Vin/L (1)
[0056] Specifically, the choke coil current increases in a linear
manner. In the descriptions below, a period when both of the first
and second switching elements Q1 and Q2 are turned ON is taken as a
period .alpha..
[0057] FIG. 3A shows a path of current passing through the circuit
when the first switching element Q1 is turned ON and the second
switching element Q2 is turned OFF in the present embodiment. FIG.
3B shows an equivalent circuit when the first switching element Q1
is in an ON state and the second switching element Q2 is in an OFF
state in the present embodiment. The DCDC converter 10 is in a
steady state and an output voltage Vout which is outputted from the
second coil L2 of the transformer Tr is equal to the capacitive
load voltage Vc. Under these conditions, whether the voltage
applied to the choke coil 11 has a positive value or a negative
value depends on the magnitude relationship between a value
obtained by dividing the capacitive load voltage Vc by a turn ratio
N and a value of the input voltage Vin. When the voltage applied to
the choke coil 11 has a positive value, the choke coil current
increases, but when having a negative value, decreases. In the
present embodiment, when the first switching element Q1 is turned
OFF and the second switching element Q2 is turned ON as well, the
equivalent circuit will be similar to the one shown in FIG. 3B. In
the following descriptions, a period in which either one of the
first and second switching elements Q1 and Q2 is turned ON is taken
as a period .beta..
[0058] The increase .DELTA.I per unit time [A/s] in the choke coil
current is expressed by the following equation (2).
.DELTA.I=(Vin-Vc/N)/L (2)
[0059] Specifically, when the value of the input voltage Vin is
larger than the value obtained by dividing the capacitive load
voltage Vc by the turn ratio N, the increase .DELTA.I has a
positive value and thus the choke coil current increases. On the
other hand, when the value of the input voltage Vin is smaller than
the value obtained by dividing the capacitive load voltage Vc by
the turn ratio N, the increase .DELTA.I has a negative value and
thus the choke coil current decreases. This means that when the
capacitive load voltage Vc is small, such as when charge of the
capacitive load 30 is started, the capacitive load 30 is charged in
the period .beta. as well. In contrast, when charge of the
capacitive load 30 progresses and the capacitive load voltage Vc is
increased, the choke coil current decreases and the charging rate
in the period .beta. is lowered.
[0060] When both of the first and second switching elements Q1 and
Q2 are turned OFF, a back electromotive voltage having reverse
polarity to the input voltage Vin is generated in the choke coil
11, which will decrease the choke coil current. In the following
description, the period in which both the first and second
switching elements Q1 and Q2 are in an OFF state is taken as a
period .gamma..
[0061] The the first and second switching elements Q1 and Q2 are
controlled in a first mode, a second mode, and a third mode where a
control cycle has a length Ts. In the first, second and third
modes, Duty values are different. Each Duty value is obtained by
dividing the length of the ON-state period of the first switching
element Q1 and the length of the ON-state period of the second
switching element Q2 by the length Ts of the control cycle. The
first, second and third modes are switched on the basis of the
magnitude relationship of a first predetermined value V1 and a
second predetermined value V2, which is smaller than the first
predetermined value V1, against the value of the capacitive load
voltage Vc.
[0062] Specifically, when the capacitive load voltage Vc is not
larger than the second predetermined value V2, the control is
performed in the first mode. When the capacitive load voltage Vc is
larger than the second predetermined value V2 but not larger than
the first predetermined value V1, the control is performed in the
second mode. When the capacitive load voltage Vc is larger than the
first predetermined value V1, the control is performed in the third
mode.
[0063] The second predetermined value V2 is set so as to increase
the current passing through the choke coil 11 in the period .beta..
That is, the second predetermined value V2 is set in such a way
that the increase .DELTA.I expressed by (2) has a positive value.
On the other hand, the first predetermined value V1 is set so as to
decrease the current passing through the choke coil 11 in the
period .beta.. That is, the first predetermined value V1 is set in
such a way that the increase .DELTA.I expressed by (2) has a
negative value.
[0064] FIG. 4 shows a series of processing steps performed by the
pulse generation unit 17 according to the present embodiment in
this case. Referring to a flow chart shown in FIG. 4, the present
process will be described. The process according to the flow chart
of FIG. 4 is performed at a predetermined control cycle.
[0065] In the power conversion apparatus 1 according to the present
embodiment, it is determined, firstly, whether or not an activation
request has been acquired (S101). A command signal for the
activation request is sent, for example, from the ECU or the like,
which is a higher-order control device. In the power conversion
apparatus 1, if it is determined that an activation request has not
acquired (NO at S101), the series of control processing steps is
not performed but a standby state is kept.
[0066] In contrast, in the power conversion apparatus 1, if it is
determined that an activation request has been acquired (YES at
S101), the capacitive load voltage Vc is acquired (S102) and it is
determined whether or not the capacitive load voltage Vc not larger
than the second predetermined value V2 (S103). As a result, in the
power conversion apparatus 1, if it is determined that the
capacitive load voltage Vc is not larger than the second
predetermined value V2 (YES at S103), the control is performed in
the first mode (S104). In contrast, in the power conversion
apparatus 1, if it is determined that the capacitive load voltage
Vc is larger than the second predetermined value V2 (NO at S103),
it is determined subsequently whether or not the capacitive load
voltage Vc is not larger than the first predetermined value V1
(S105). As a result, in the power conversion apparatus 1, if it is
determined that the capacitive load voltage Vc is not larger than
the first predetermined value V1 (YES at S105), the control is
performed in the second mode (S106). In contrast, in the power
conversion apparatus 1, if it is determined that the capacitive
load voltage Vc is larger than the first predetermined value V1 (NO
at S105), the control is performed in the third mode (S107).
[0067] Subsequently, in the power conversion apparatus 1, after
performing control of any of the first, second and third modes
during predetermined time, a determination is made as to
termination of the control process (S108). In the determination
processing step (S108), for example, it is only required to
re-acquire the capacitive load voltage Vc and determine whether or
not the capacitive load voltage Vc has become equal to or larger
than a predetermined upper limit. The determination as to whether
the capacitive load voltage Vc has become equal to or larger than a
predetermined upper limit may be performed after the capacitive
load voltage Vc has been determined to be larger than the first
predetermined value V1 (NO at S105). As a result, in the power
conversion apparatus 1, if the control process is determined to be
terminated (YES at S108), the series of control processing steps is
terminated and the control waits until an activation request is
made. In contrast, in the power conversion apparatus 1, if the
control process is determined not to be terminated (NO at S108), it
is determined whether or not a termination request has been
acquired (S109). A command signal for the termination request is
sent from a high-order control device, such as the ECU. In the
power conversion apparatus 1, if it is determined that a
termination request has been acquired (YES at S109), the series of
control processing steps is terminated and the control waits until
an activation request is made. In contrast, in the power conversion
apparatus 1, if it is determined that a termination request has not
been acquired (NO at S109), the control returns to the processing
step for acquiring the capacitive load voltage Vc (S102) to
reiterate the processing steps onward.
[0068] Although the flow chart of FIG. 4 shows only the processing
steps related to the charge control for the capacitive load 30, the
DCDC converter 10 also controls power conversion and the like,
besides the charge control for the capacitive load 30.
Specifically, the controls performed by the DCDC converter 10 may
include, for example, a control under which power supplied via the
connecting terminals 40a and 40b is stepped down to charge the
secondary battery 20. Since the control is well known, a detailed
description is omitted.
[0069] FIG. 5A shows the first PWM signal as a driving signal of
the first switching element Q1, and the second PWM signal as a
driving signal of the second switching element Q2, in performing
the control in the first mode in the present embodiment. In the
first mode, a phase difference between the first and second PWM
signals is Ts/2 which is half of the control cycle (half-cycle). In
both of the first and second PWM signals, one control cycle is
composed of an ON-state period in indicated by a length T1 and an
OFF-state period in indicated by a length (Ts-T1). In this case,
the length T1 of the ON-state period is less than Ts/2. That is, a
Duty value indicated by T1/Ts is less than 0.5. Accordingly, in the
first mode, the period .beta. of the length T1 and the period
.gamma. of the length (Ts/2-T1) are alternated.
[0070] In the first mode, in the period .beta., the capacitive load
30 is charged and the choke coil current increases. On the other
hand, in the first mode, in the period .gamma., the choke coil
current increased in the period .beta. is consumed in the circuit.
The length T1 in an ON-state period is set such that the choke coil
current becomes zero in the period .gamma..
[0071] FIG. 5B shows the first PWM signal as a driving signal of
the first switching element Q1, and the second PWM signal as a
driving signal of the second switching element Q2, when the control
is performed in the second mode in the present embodiment. In the
second mode, the phase difference between the first and second PWM
signals is Ts. In both the first and second PWM signals, a first
control cycle and a second control cycle are alternated. The first
control cycle is started from an ON-state period indicated by a
length T2h and is terminated with an OFF-state period indicated by
a length (Ts-T2h). The second control cycle is started from an
ON-state period indicated by a length T2l and is terminated with an
OFF-state period indicated by a length (Ts-T2l). That is, the time
point when the ON-state period of the length T2h of the first PWM
signal is started coincides with the time point when the ON-state
period of the length T2l of the second PWM signal is started. In
addition, the time point when the ON-state period of the length T2l
of the first PWM signal is started coincides with the time point
when the ON-state period of the length T2h of the second PWM signal
is started. Further, summation of the value of T2h/Ts as the first
Duty value in the first control cycle, and the value of T2l/Ts as
the second Duty value in the second control cycle, is less than
1.
[0072] Accordingly, during one control cycle of the second mode,
the period .alpha. of the length T2l, the period .beta. of the
length (T2h-T2l), and the period .gamma. of the length (Ts-T2h) are
repeated in this order.
[0073] In the period .alpha. of the second mode, the choke coil
current increases. In the period .beta. of the second mode, the
choke coil current increases or decreases on the basis of the
magnitude relationship between the value obtained by dividing the
capacitive load voltage Vc by a turn ratio N and the value of the
input voltage Vin. In the period .gamma. of the second mode, the
choke coil current increased in the periods .alpha. and .beta., or
the choke coil current not reduced to zero in the period .beta., is
consumed in the circuit. The lengths T2h and T2l of the ON-state
period are set such that the choke coil current becomes zero in the
period .gamma..
[0074] FIG. 5C shows the first PWM signal as a driving signal of
the first switching element Q1 and the second PWM signal as a
driving signal of the second switching element Q2 in performing the
control in the third mode of the present embodiment. In the third
mode, the phase difference between the first and second PWM signals
is Ts/2. In both the first and second PWM signals, one control
cycle is composed of an ON-state period indicated by a length T3
and an OFF-state period indicated by a length (Ts-T3). In this
case, the length T3 of the ON-state period is larger than Ts/2
which is half the length of the control cycle. That is, a Duty
value indicated by T3/Ts is larger than 0.5. Accordingly, in the
third mode, the period .alpha. of a length (T3-Ts/2) and the period
.beta. of the length (Ts-T3) are alternated.
[0075] In the period .alpha. of the third mode, the choke coil
current increases. In contrast, in the period .beta. of the third
mode, the choke coil current decreases, and with the decrease of
the choke coil current, the capacitive load 30 is charged. The
length T3 of the ON-state period is set such that the increase in
the choke coil current in the period .alpha. is equal to the
decrease in the choke coil current in the period .beta..
[0076] A Duty value in the third mode, which is Duty3 having a
value more than 0.5, is changed with the progress of charging of
the capacitive load 30. The Duty3 is set to Duty0 that is an
initial value larger than 0.5 when the second mode is switched to
the third mode.
[0077] In the third mode, the increase of current in the period
.alpha. is equal to the decrease of current in the period .beta..
Accordingly, a value zero is resulted from the summation of a value
obtained by multiplying the increase of current per unit time in
the period .alpha. (.DELTA.I in (1)) by the length (T3-Ts/2) in the
period .alpha. and a value obtained by multiplying the increase of
current per unit time in the period .beta. (.DELTA.I in (2)) by the
length (Ts-T3) in the period .beta.. Thus, the equation (3) is
obtained. In this case, the capacitive load voltage Vc and the
output voltage Vout are assumed to be different. Accordingly, in
(2), the capacitive load voltage Vc is substituted by the output
voltage Vout.
(T3-Ts/2).times.Vin+(Ts-T3).times.(Vin-Vout/N)=0 (3)
[0078] In the present embodiment, using Duty3 that is the Duty
value of the PWM signal in the third mode, (3) is transformed. As a
result, the output voltage Vout of the transformer Tr is expressed
by the following equation (4).
Vout=N.times.Vin/(2.times.(1-Duty3)) (4)
[0079] There may occur divergence between the output voltage Vout
and the capacitive load voltage Vc when the second mode is switched
to the third mode. In such a case, when the circuit is assumed to
be an ideal circuit with no resistance, an inrush current of
infinite magnitude is unavoidably caused. In this case, if the
circuit is not an ideal circuit, an inrush current is likely to be
caused.
[0080] In this regard, in the present embodiment, the first
predetermined value V1 serving as a condition for switching the
second mode to the third mode, is set as follows. In the present
embodiment, when the second mode is switched to the third mode, the
first predetermined value V1 is set by the following equation (5)
using Duty0 mentioned above in such a way that the first
predetermined value V1 as a threshold of the capacitive load
voltage Vc is equal to the output voltage Vout.
V1=N.times.Vin/(2.times.(1-Duty0)) (5)
[0081] Specifically, in the present embodiment, the first
predetermined value V1 that is a value of the capacitive load
voltage Vc when the second mode is switched to the third mode is
ensured to be equal to the output voltage Vout of the transformer
Tr.
[0082] As described above, the value of Duty3 as a Duty value in
the third mode is changed with the progress of charging of the
capacitive load 30. Therefore, when divergence occurs between the
output voltage Vout and the capacitive load voltage Vc with the
change of the value of Duty3 and when the circuit is assumed to be
an ideal circuit with no resistance, an inrush current having an
infinite magnitude is unavoidably caused. In this case, if the
circuit is not an ideal circuit, an inrush current is likely to be
caused. Therefore, in the present embodiment, (4) is transformed by
substituting the output voltage Vout by the capacitive load voltage
Vc. In the present embodiment, the value of Duty3 is set by the
following equation (6) obtained by the transformation.
Duty3=1-N.times.Vin/(2.times.Vc) (6)
[0083] That is, in the present embodiment, Duty3 is set in such a
way that the capacitive load voltage Vc is equal to the output
voltage Vout of the transformer Tr.
[0084] Depending on the initial value and the target value of the
capacitive load voltage Vc, not all of the first to third modes are
performed. That is, when an initial value of the capacitive load
voltage Vc is not larger than the second predetermined value V2 and
a target value of the capacitive load voltage Vc is larger than the
first predetermined value V1, charge is performed in the first to
third modes. In contrast, the following controls will be performed
when at least one of the following conditions is satisfied, the
conditions being that the initial value of the capacitive load
voltage Vc is larger than the second predetermined value V2 and
that the target value of the capacitive load voltage Vc is not
larger than the first predetermined value V1.
[0085] When the target value of the capacitive load voltage Vc is
not larger than the second predetermined value V2, charge is
started in the first mode without transition to another mode, and
thus the charge is terminated in the first mode.
[0086] When the initial value of the capacitive load voltage Vc is
not larger than the second predetermined value, and the target
value of the capacitive load voltage Vc is larger than the second
predetermined value V2 but not larger than the first predetermined
value V1, charge is started in the first mode without routing
through the third mode, and thus the charge is terminated in the
second mode.
[0087] When the initial value of the capacitive load voltage Vc is
larger than the second predetermined value V2 but not larger than
the first predetermined value V1, and the target value of the
capacitive load voltage Vc is larger than the second predetermined
value V2 but not larger than the first predetermined value V1,
charge is started in the second mode without transition to another
mode, and thus the charge is terminated in the second mode.
[0088] When the initial value of the capacitive load voltage Vc is
larger than the second predetermined value V2 but not larger than
the first predetermined value V1, and the target value of the
capacitive load voltage Vc is larger than the first predetermined
value V1, charge is started in the second mode without routing
through the first mode, and thus the charge is terminated in the
third mode.
[0089] When the initial value of the capacitive load voltage Vc is
a value larger than the first predetermined value V1, charge is
started in the third mode without transition to another mode, and
thus the charge is terminated in the third mode.
[0090] With the above configuration, the power conversion apparatus
1 according to the present embodiment exhibits the following
advantageous effects.
[0091] In the power conversion apparatus 1 according to the present
embodiment, when the capacitive load voltage Vc is small, such as
when charge to the capacitive load 30 is started, a control in the
first mode is performed. Thus, the power conversion apparatus 1 is
provided with the period .beta. in which either one of the first
and second switching elements Q1 and Q2 is turned OFF, and the
period .gamma. in which both of the first and second switching
elements Q1 and Q2 are turned OFF. Therefore, in the power
conversion apparatus 1 according to the present embodiment, the
current increased in the choke coil 11 in the period .beta. can be
decreased in the period .gamma.. Thus, the power conversion
apparatus 1 can prevent the current passing through the choke coil
11 from being kept increasing. As a result, degradation and failure
of the DCDC converter 10 may be minimized.
[0092] In the power conversion apparatus 1 according to the present
embodiment, when the capacitive load voltage Vc is larger than the
second predetermined value V2, the control in the second mode is
performed. Thus, the power conversion apparatus 1 is provided with
the period .alpha. in which both the first and second switching
elements Q1 and Q2 are turned ON, the period .beta. in which either
one of the first and second switching elements Q1 and Q2 is OFF,
and the period .gamma. in which both the first and second switching
elements Q1 and Q2 are turned OFF. Therefore, in the power
conversion apparatus 1 according to the present embodiment, the
current passing through the choke coil 11 in the period .alpha. can
be increased and the charging rate for the capacitive load 30 can
be improved. In the power conversion apparatus 1, the current in
the choke coil 11 can be decreased in the period .gamma.. Thus, the
power conversion apparatus 1 can prevent the current passing
through the choke coil 11 from being kept increasing. As a result,
degradation and failure of the DCDC converter 10 can be
minimized.
[0093] In the power conversion apparatus 1 according to the present
embodiment, when the capacitive load voltage Vc is larger than the
first predetermined value V1, such as when charge of the capacitive
load 30 is progressing, the control in the third mode is performed.
Thus, the power conversion apparatus 1 is provided with the period
.alpha. in which both the first and second switching elements Q1
and Q2 are turned ON, and the period .beta. in which either one of
the first and second switching elements Q1 and Q2 is turned ON.
Accordingly, in the power conversion apparatus 1, the current
passing through the choke coil 11 in the period .alpha. can be
increased, and the current passing through the choke coil 11 in the
period .beta. can be decreased. With this configuration, in the
power conversion apparatus 1 according to the present embodiment,
the capacitive load 30, in which charge is progressing, can be
rapidly charged.
[0094] When the capacitive load voltage Vc exceeds the first
predetermined value V1, there may be a difference between the
output voltage Vout of the transformer Tr and the capacitive load
voltage Vc. In such a case, when the circuit is assumed to be an
ideal circuit having no resistance, an inrush current is likely to
be caused, which leads to a high probability of causing damage to
the circuit. In the power conversion apparatus 1 according to the
present embodiment, the first predetermined value V1 is set such
that the output voltage Vout is equal to the capacitive load
voltage Vc when the capacitive load voltage Vc exceeds the first
predetermined value V1. Therefore, in the power conversion
apparatus 1, there is no potential difference between the output
voltage Vout of the transformer Tr and the capacitive load voltage
Vc. With this configuration, the power conversion apparatus 1
according to the present embodiment can minimize the occurrence of
an inrush current.
[0095] When the control of the third mode is performed, there may
be a difference between the output voltage Vout of the transformer
Tr and the capacitive load voltage Vc. In such a case, when the
circuit is assumed to be an ideal circuit having no resistance, an
inrush current is likely to be cause, which leads a high
probability of causing damage to the circuit. In the power
conversion apparatus 1 according to the present embodiment, when
the control of the third mode is performed, Duty3 as a Duty value
in the third mode is set such that the output voltage Vout is equal
to the capacitive load voltage Vc. Therefore, in the power
conversion apparatus 1, there is no potential difference between
the output voltage Vout of the transformer Tr and the capacitive
load voltage Vc. With this configuration, the power conversion
apparatus 1 according to the present embodiment can minimize the
occurrence of an inrush current.
Second Embodiment
[0096] A power conversion apparatus according to the present
embodiment corresponds to a circuit similar to the power conversion
apparatus 1 of the first embodiment, but the control method is
different. In the power conversion apparatus according to the
present embodiment, the control of the second mode is not
performed. In the power conversion apparatus according to the
present embodiment, charge is performed in the first mode while the
capacitive load voltage Vc is not larger than the first
predetermined value V1, and charge is performed in the third mode
when the capacitive load voltage Vc becomes larger than the first
predetermined value V1. The first predetermined value V1 and the
value of Duty3 as a Duty value in the third mode are set in a
manner similar to the first embodiment.
[0097] In the present embodiment, it is not necessarily that both
of the first and third modes are performed, depending on the
initial value and the target value of the capacitive load voltage
Vc. Specifically, charge is performed in the first and third modes
when the initial value of the capacitive load voltage Vc is not
larger than the first predetermined value V1 but the target value
of the capacitive load voltage Vc is larger than the first
predetermined value V1. In contrast, when the initial value of the
capacitive load voltage Vc is larger than the first predetermined
value V1, or when the target value of the capacitive load voltage
Vc is not larger than the first predetermined value V1, the
following controls are performed.
[0098] When the initial value of the capacitive load voltage Vc is
larger than the first predetermined value V1, charge is started in
the third mode without transition to another mode, and thus the
charge is terminated in the third mode.
[0099] When the target value of the capacitive load voltage Vc not
larger than is the first predetermined value V1, charge is started
in the first mode without transition to another mode, and thus the
charge is terminated in the first mode.
[0100] With the above configuration, the power conversion apparatus
according to the present embodiment exhibits advantageous effects
similar to those of the first embodiment.
Third Embodiment
[0101] FIG. 6 shows a circuit diagram of a power conversion
apparatus according to the present embodiment. A power conversion
apparatus 3 according to the present embodiment includes, similar
to the power conversion apparatus 1 according to the first
embodiment, a DCDC converter 10, and a secondary battery 20 serving
as a direct current power supply connected to the input terminals
of the DCDC converter 10. Further, the power conversion apparatus 3
includes a capacitive load 30 (smoothing capacitor) connected
parallel to the output terminals of the DCDC converter 10, and
connecting terminals 40a and 40b provided to the output terminals
of the DCDC converter 10.
[0102] The DCDC converter 10 is provided with a choke coil 11, a
transformer Tr, a bridge circuit 14, a first switching element Q1,
and a second switching element Q2.
[0103] The transformer Tr is composed of a first coil L1 and a
second coil L2 that are magnetically coupled to each other, with
the first coil L1 being provided with the center tap 13. The second
coil L2 is connected to the capacitive load 30 via the bridge
circuit 14 and the output terminals of the DCDC converter 10.
[0104] The first switching element Q1 and the second switching
element Q2 are MOSFETs. Among both ends of the first coil L1, one
end is connected to a drain of the first switching element Q1 and
the other end to a drain of the second switching element Q2. On the
other hand, both a source of the first switching element Q1 and a
source of the second switching element Q2 are connected to a
predetermined connecting point 12. The predetermined connecting
point 12 is connected to a negative terminal of the secondary
battery 20 via an input terminal of the DCDC converter 10. The
choke coil 11 has an input terminal connected to a positive
terminal of the secondary battery 20 via an input terminal of the
DCDC converter 10, and an output terminal connected to the center
tap 13. The first switching element Q1 and the second switching
element Q2 have a first parasitic diode D1 and a second parasitic
diode D2, respectively, which are in reverse parallel connection.
Thus, the power conversion apparatus 3 according to the present
embodiment is different from the first embodiment in the connecting
configuration of the first and second switching elements Q1 and Q2
to the first coil L1.
[0105] In the power conversion apparatus 3 according to the present
embodiment, a control similar to the power conversion apparatus 1
of the first embodiment, or a control similar to the power
conversion apparatus of the second embodiment is performed. Thus,
the power conversion apparatus 3 according to the present
embodiment exhibits advantageous effects similar to those the above
embodiments.
Fourth Embodiment
[0106] A power conversion apparatus according to the present
embodiment uses a circuit similar to the power conversion apparatus
1 of the first embodiment, or the power conversion apparatus 3 of
the third embodiment, but a method of setting a Duty value in the
first mode and a method of setting a Duty value in the second mode
are different from the first to third embodiments. For the choke
coil current, the present embodiment is provided with a maximum
value which is less likely to cause degradation or the like of the
DCDC converter 10 and allowable (maximum allowable value).
Specifically, in the present embodiment, a first maximum allowable
value Imax1 is provided to the first mode and a second maximum
allowable value Imax2 is provided to the second mode. The first and
second maximum allowable values Imax1 and Imax2 are memorized, for
example, in a memory of the ECU or the like.
[0107] FIG. 7 shows a relationship between the Duty value and the
first maximum allowable value Imax1 in the first mode of the
present embodiment. In the first mode, Duty' is set by the
following equation (7) in such a way that the first maximum
allowable value Imax1 is ensured to be a value obtained by
multiplying an increase .DELTA.I in the current per unit time in
the period .beta., expressed by (2), by the length T1 in the period
.beta.. In this case, the length T1 in the period .beta. is
expressed as a product (Duty1Ts) of Ts as the length of the control
cycle, and Duty 1 as a Duty value. The input voltage Vin, the
capacitive load voltage Vc, and L as a self-inductance of the choke
coil 11 are constant in the period .beta..
Duty1=Imax1.times.L/{Ts(Vin-Vc/N)} (7)
[0108] Accordingly, in the first mode, the choke coil current
becomes the first maximum allowable value Imax1 after turning ON
the first and second switching elements Q1 and Q2 and after lapse
of time corresponding to the length T1 of the period .beta..
[0109] FIG. 8 shows the Duty value and the second maximum allowable
value Imax2 in the second mode of the present embodiment. In the
second mode, Duty2l as a Duty value in the period .alpha., and
Duty2h as a Duty value corresponding to a sum of the periods
.alpha. and .beta. are set in such a way that the second maximum
allowable value Imax2 is ensured to be a sum of an increase in the
choke coil current in the period .alpha. and an increase in the
choke coil current in the period .beta..
[0110] The increase in the choke coil current in the period .alpha.
is obtained by multiplying the increase .DELTA.I of current per
unit time in the period .alpha. expressed by (1), by the length T2l
of the period .alpha.. In this case, the length T2l of the period
.alpha. is expressed as a product (Duty2lTs) of Ts as the length of
the control cycle, and Duty2l as a Duty value. Therefore, in the
second mode, Duty2l is set by the following equation (8) in such a
way that the increase in the choke coil current in the period
.alpha. is smaller than the second maximum allowable value
Imax2.
Duty2l<Imax2.times.L/(Ts.times.Vin) (8)
[0111] On the other hand, the increase in the choke coil current in
the period .beta. is obtained by multiplying the increase .DELTA.I
of current per unit time in the period .beta. expressed by (2), by
the length (T2h-T2l) of the period p. In this case, the length T2h
of the period .beta. is expressed as a product {(Duty2h-Duty2l)Ts}
of Ts as the length of the control cycle, and a difference in the
Duty value (Duty2h-Duty2l). Thus, in the second mode, Duty2h is set
by the equation (9) in such a way that the second maximum allowable
value Imax2 is ensured to be a sum of the increase in the choke
coil current in the period .alpha. and the increase in the choke
coil current in the period .beta.. In this case, for Duty2l that is
a Duty value in the period a, the value set by (8) is used. The
input voltage Vin, the capacitive load voltage Vc, and L as the
self-inductance of the choke coil 11 are constant in the periods
.alpha. and .beta..
Duty2h={(Imax2.times.L-Vin.times.Duty2l.times.Ts)/{Ts(Vin-Vc/N)}}+Duty2l
(9)
[0112] Accordingly, in the second mode, the choke coil current
becomes the second maximum allowable value Imax2 after turning on
the first and second switching elements Q1 and Q2 and after lapse
of time corresponding to the length T2h that is a sum of the
periods .alpha. and .beta..
[0113] The first and second maximum allowable values Imax1 and
Imax2 may be the same, or may be different from each other. When
the setting of a Duty value of the present embodiment is applied to
the power conversion apparatus of the second embodiment, the
setting of Duty1 described above may only have to be performed in
respect of the control of the first mode.
[0114] With the above configuration, the power conversion apparatus
according to the present embodiment exhibits the following
advantageous effects, besides the advantageous effects similar to
those of the above embodiments.
[0115] In the first and second modes of the power conversion
apparatus according to the present embodiment, Duty1, Duty2l, and
Duty2h, as Duty values, are set in such a way that the choke coil
current does not exceed the first and second maximum allowable
values Imax1 and Imax2. Thus, in the power conversion apparatus
according to the present embodiment, the choke coil current is not
excessively increased to thereby minimize degradation or failure of
the DCDC converter 10.
Fifth Embodiment
[0116] A power conversion apparatus according to the present
embodiment uses a circuit similar to the power conversion apparatus
1 of the first embodiment or the power conversion apparatus 3 of
the third embodiment, but the control method is different from the
first to third embodiments. In the present embodiment, the control
of the first to third modes is performed in a manner similar to the
first embodiment, but the respective modes have control signals
different from each other.
[0117] FIG. 9A shows control signals in a first mode in the present
embodiment. In the first mode, control signals are transmitted to
first and second switching elements Q1 and Q2 at a common control
cycle Ts, and control signals are transmitted with a mutual phase
difference being a half of the control cycle Ts. The control
signals instruct the first and second switching elements Q1 and Q2
to make a state transition to either one of ON- and OFF-states. The
signal instructing a state transition to an ON-state (ON driving)
is an ON signal, and the signal instructing a state transition to
an OFF-state (OFF driving) is an OFF signal.
[0118] In the control signals transmitted to the first and second
switching elements Q1 and Q2, an ON-state period with a length T1
(<Ts/4) and an OFF-state period with a length (Ts/4-T1) are
alternated on a two-by-two basis in a half of the control cycle Ts.
In the control signals, an OFF-state is kept in the subsequent half
cycle (first predetermined period).
[0119] Specifically, under the control of the first mode, in a half
of the control cycle Ts, one of the first and second switching
elements Q1 and Q2 is kept in an OFF-state, and the other switching
element is ensured to alternate an ON-state with an OFF-state. In
this way, similar to the first embodiment, the present embodiment
can alternate the period .beta. in which one of the first and
second switching elements Q1 and Q2 is in an ON-state and the other
switching element is in an OFF-state, with the period .gamma. in
which both of the first and second switching elements Q1 and Q2 are
in an OFF-state.
[0120] FIG. 9B shows control signals in a second mode of the
present embodiment. In the second mode, control signals are
transmitted to first and second switching elements Q1 and Q2 at a
common control cycle Ts, and control signals are transmitted with a
mutual phase difference being a half of the control cycle Ts.
[0121] In the control signals transmitted to the first and second
switching elements Q1 and Q2, in a half of the control cycle Ts, an
ON-state period of a length T2h (<Ts/4) is alternated with an
OFF-state period of a length (Ts/4-T2h) on a two-by-two basis. In
the subsequent half cycle of the control signals (first
predetermined period), an ON-state period of a length T2l
(<Ts/4) is alternated with an OFF-state period of a length
(Ts/4-T2l) on a two-by-two basis. In this case, in each of the
control signals transmitted to the first and second switching
elements Q1 and Q2, a time point when the ON-state period of the
length T2h is started and a time point when the ON-state period of
the length T2l is started are mutually offset by half a cycle
(Ts/2). Accordingly, the time point when the ON-state period of the
first switching element Q1 is started coincides with the time point
when the ON-state period of the second switching element Q2 is
started.
[0122] In this way, similar to the first embodiment, the present
embodiment, sequentially repeat the period .alpha. in which both of
the first and second switching elements Q1 and Q2 are in an
ON-state, the period .beta. in which one of the first and second
switching elements Q1 and Q2 is in an ON-state and the other
switching element is in an OFF-state, and the period .gamma. in
which both of the first and second switching elements Q1 and Q2 are
in an OFF-state.
[0123] FIG. 9C shows control signals in a third mode of the present
embodiment. In the third mode, control signals are transmitted to
first and second switching elements Q1 and Q2 at a common control
cycle Ts, and control signals are transmitted with a mutual phase
difference being a half of the control cycle Ts.
[0124] In the control signals transmitted to the first and second
switching elements Q1 and Q2, in a half of the control cycle Ts, an
ON-state period of a length T3' (<Ts/4) is alternated with an
OFF-state period of a length (Ts/4-T3') on a two-by-two basis. In
the subsequent half cycle of the control signals (first
predetermined period), the ON-state is kept.
[0125] Specifically, under the control of the third mode, in a half
of the control cycle Ts, one of the first and second switching
elements Q1 and Q2 is kept in an ON-state and the other switching
element is permitted to alternate an ON-state and an OFF-state. In
this way, similar to the first embodiment, the present embodiment
can alternate the period .alpha. in which both of the first and
second switching elements Q1 and Q2 are in an ON-state, with the
period .beta. in which one of the first and second switching
elements Q1 and Q2 is in an ON-state and the other switching
element is in an OFF-state.
[0126] In the present embodiment, in each of the first to third
modes, the ON-state period is provided twice during a half of the
control cycle Ts. Alternatively, the ON-state period may be
provided three or more times.
[0127] Further, the length of the ON-state period of the first and
second switching elements Q1 and Q2 in each of the first to third
modes only has to be set in a manner similar to the first
embodiment. Alternatively, the length of the ON-state period of the
first and second switching elements Q1 and Q2 in each of the first
and second modes may be set in a manner similar to the fourth
embodiment.
[0128] In the present embodiment, similar to the second embodiment,
the control in the first and third modes may be performed, and the
second mode may be ensured not to be performed.
[0129] With the above configuration, the power conversion apparatus
according to the present embodiment exhibits the advantageous
effects similar to those of the above embodiments.
Sixth Embodiment
[0130] A power conversion apparatus according to the present
embodiment uses a circuit similar to the power conversion apparatus
1 of the first embodiment or the power conversion apparatus 3 of
the third embodiment, but the control method is different from the
first to third embodiments. In the present embodiment, control of
the first to third modes is performed similar to the first
embodiment, but the control signals in the respective modes are
different.
[0131] FIGS. 10A to 10C show control signals in the first to third
modes in the present embodiment.
[0132] FIG. 10A shows control signals in the first mode of the
present embodiment. As shown in FIG. 10A, in a predetermined period
from t0 to t2 (first predetermined period) of the first mode, an
OFF-state of the second switching element Q2 is kept, while an
ON-state and an OFF-state of the first switching element Q1 are
alternated. In a predetermined period from t1 to t4 (first
predetermined period) of the first mode, an OFF-state of the first
switching element Q1 is kept, while an ON-state and an OFF-state of
the second switching element Q2 are alternated. Further, in a
predetermined period from t3 to t5 (first predetermined period) of
the first mode, an OFF state of the second switching element Q2 is
kept, while an ON-state and an OFF-state of the first switching
element Q1 are alternated.
[0133] In this case, the predetermined period in which the
OFF-state of the first switching element Q1 is kept, and the
predetermined period in which the OFF-state of the second switching
element Q2 is kept may have the same length, or may have different
lengths. The predetermined periods in which the OFF-state of the
first switching element Q1 is kept may have the same length, or may
have different lengths. The same applies to the predetermined
periods in which the OFF-state of the second switching element Q2
is kept. Further, while one of the first and second switching
elements Q1 and Q2 is in an OFF-state, an ON-state and an OFF-state
of the other switching element may be alternated by any number
times. While one of the first and second switching elements Q1 and
Q2 is in an OFF-state, the periods in which an ON-state and an
OFF-state of the other switching element are alternated may have
the same length, or may have different lengths. For example, as
shown in FIG. 10A, in the predetermined period from t0 to t2 (first
predetermined period) in an OFF-state of the second switching
element Q2, the first switching element Q1 may be in an ON-state
once or twice. In the predetermined period from t1 to t4 (first
predetermined period) in an OFF-state of the first switching
element Q1, the second switching element Q2 may be in an ON-state
several times.
[0134] Specifically, under the control of the first mode, the state
where one of the first and second switching elements Q1 and Q2 is
kept in an OFF-state is alternated with the state where the other
switching element is alternately in an ON-state and an OFF-state.
In this way, in the present embodiment, similar to the first
embodiment, the period .beta. in which one of the first and second
switching elements Q1 and Q2 is in an ON-state and the other
switching element is in an OFF-state can be alternated with the
period .gamma. in which both of the first and second switching
elements Q1 and Q2 are in an OFF-state.
[0135] FIG. 10B shows control signals in the second mode of the
present embodiment. As shown in FIG. 10B, in the second mode, both
of the first and second switching elements Q1 and Q2 are turned ON
at t0, the second switching element Q2 is turned OFF at t1, and the
first switching element Q1 is turned OFF at t2. The OFF-state
periods of the first and second switching elements Q1 and Q2 are
kept until t3. Accordingly, a predetermined period from t0 to t1 is
the period .alpha. in which both the first and second switching
elements Q1 and Q2 are in an ON-state. A predetermined period from
t1 to t2 is the period .beta. in which one of the first and second
switching elements Q1 and Q2 is in an ON-state. A predetermined
period from t2 to t3 is the period .gamma. in which both the first
and second switching elements Q1 and Q2 are in an OFF-state.
Similarly, in the second mode, both of the first and second
switching elements Q1 and Q2 are turned ON at t3, the second
switching element Q2 is turned OFF at t4, and the first switching
element Q1 is turned OFF at t5. The OFF-states of the first and
second switching elements Q1 and Q2 are kept until t6.
[0136] Subsequently, in the second mode, both the first and second
switching elements Q1 and Q2 are turned ON at t6, the first
switching element Q1 is turned OFF at t7, and the second switching
element Q2 is turned OFF at t8. Therefore, the switching element
which is in an ON-state in the period .beta. from t7 to t8 is
different from the one in the periods .beta. from t1 to t2 and from
t4 to t5.
[0137] under the control of the second mode, one of the first and
second switching elements Q1 and Q2 may be turned OFF first at all
times.
[0138] Specifically, the control of the second mode enables
sequential repetition of the state where both of the first and
second switching elements Q1 and Q2 are in an ON-state, the state
where one of the first and second switching elements Q1 and Q2 is
an ON-state and the other switching element is in an OFF-state, and
the state where both of the first and second switching elements Q1
and Q2 are in an ON-state.
[0139] FIG. 10C shows control signals in the first mode of the
present embodiment. As shown in FIG. 10C, in a predetermined period
from t0 to t2 (second predetermined period) of the third mode, an
ON-state of the second switching element Q2 is kept, while an
ON-state and an OFF-state of the first switching element Q1 are
alternated. In addition, in a predetermined period of t1 onward
(second predetermined period) of the third mode, an ON-state of the
first switching element Q1 is kept, while an ON-state and an
OFF-state of the second switching element Q2 are alternated.
[0140] In this case, the predetermined period in which an ON-state
of the first switching element Q1 is kept and the predetermined
period in which an ON-state of the second switching element Q2 is
kept may have the same length, or may have different lengths. The
predetermined periods in which an ON-state of the first switching
element Q1 is kept may have the same length, or may have different
lengths. The same applies to the predetermined periods in which an
ON-state of the second switching element Q2 is kept. Further, while
one of the first and second switching elements Q1 and Q2 is in an
ON-state, an ON-state and an OFF-state of the other switching
element may be alternated by any number times. While one of the
first and second switching elements Q1 and Q2 is in an ON-state,
the periods in which an ON-state and an OFF-state of the other
switching element are alternated may have the same length, or may
have different lengths. For example, as shown in FIG. 10C, in the
predetermined period from t0 to t2 (second predetermined period) in
which the second switching element Q2 is in an ON-state, the first
switching element Q1 may be in an ON-state only once, or three or
more times. In the predetermined period of t1 onward (first
predetermined period) in which the first switching element Q1 is in
an ON-state, the second switching element Q2 may be in an ON-state
only once, or three or more times.
[0141] Specifically, under the control of the third mode, one of
the first and second switching elements Q1 and Q2 is kept in the ON
state, while the other switching element alternates an ON-state and
an OFF-state. In this way, in the present embodiment, the period
.alpha. in which both of the first and second switching elements Q1
and Q2 are in an ON-state can be alternated with the period .beta.
in which one of the first and second switching elements Q1 and Q2
is in an ON-state and the other switching element is in an
OFF-state.
[0142] Similar to the fourth embodiment, the ON-state period of the
first and second switching elements Q1 and Q2 in each of the first
and second modes may be set in such a way that the choke coil
current does not exceed the first and second maximum allowable
values Imax1 and Imax2. Further, the ON-state period of the first
and second switching elements Q1 and Q2 in the third mode may be
set using a method similar to the first embodiment.
[0143] The control signals shown in FIGS. 10A to 10C are only
examples. The control of the first and second switching elements Q1
and Q2 may only need to be performed in the first to third
modes.
[0144] Further, in the present embodiment, each of the first and
second switching elements Q1 and Q2 is further provided with a
timer that calculates an accumulated value of ON-state time. In the
present embodiment, the control is performed in a predetermined
period (third predetermined period) in such a way that the
accumulated value of ON-state time in the first switching element
Q1 is equal to an accumulated value of ON-state time in the second
switching element Q2. In this way, in the present embodiment, the
DCDC converter 10 is prevented from being magnetically deflected,
and loss and heat generation are equalized between the first and
second switching elements Q1 and Q2.
[0145] In this case, in each of the first to third modes, the
accumulated value of ON-state time in the first switching element
Q1 may be ensured to be equal to the accumulated value of ON-state
time in the second switching element Q2. Further, the predetermined
period (third predetermined period) may be extended over a
plurality of modes. In this case, for example, if there is a
difference, in the first mode, between the accumulated value of
ON-state time of one of the first and second switching elements Q1
and Q2, and the accumulated value of ON-state time of the other
switching element, the difference may only have to be compensated
under the control of the second or third mode.
[0146] Further, if there is a difference between the accumulated
value of ON-state time in the first switching element Q1 and the
accumulated value of ON-state time in the second switching element
Q2 at the time of terminating charge of the capacitive load 30, the
difference may only have to be compensated in performing charge the
next time.
[0147] The concept of "to be equal" in the present embodiment
refers to "be in agreement with" in a range of tolerating
predetermined errors.
[0148] With the above configuration, the power conversion apparatus
according to the present embodiment exhibits the advantageous
effects similar to those of the above embodiments.
Seventh Embodiment
[0149] A power conversion apparatus according to the present
embodiment is partially different in the circuit configuration from
the power conversion apparatus 1 of the first embodiment, and is
different in the process performed by the pulse generation unit 17.
FIG. 11 shows a circuit diagram of a power conversion apparatus
according to the present embodiment.
[0150] A power conversion apparatus 7 according to the present
embodiment is further provided with a current detecting means 19.
The current detecting means 19 detects a reactor current IL passing
through the choke coil 11, and inputs the detected current into the
pulse generation unit 17. The rest of the circuit configuration is
similar to the circuit configuration of the first embodiment and
thus the description is omitted. The rest of the circuit
configuration may be similar to the circuit configuration of the
third embodiment.
[0151] Next, referring to FIG. 12, the process performed by the
pulse generation unit 17 of the present embodiment will be
described. FIG. 12 is a block diagram illustrating the process
performed by the pulse generation unit 17 in the power conversion
apparatus 7 of the present embodiment.
[0152] A constant current control unit 50 reads, from a memory, a
first command Iref1 for the reactor current IL in the first mode, a
second command Iref2 for the reactor current IL in the second mode,
and a third command Iref3 for the reactor current IL in the third
mode, for use in the control.
[0153] The first command Iref1 is determined so that avalanche
current will not be excessive when one of the first and second
switching elements Q1 and Q2 has transitioned from an ON-state to
an OFF-state to thereby bring both of the switching elements into
an OFF-state. The avalanche current is generated on the basis of
the value of the first command Iref1. The first command Iref1 is
directly outputted from the constant current control unit 50.
[0154] The second command Iref2 may have the same value as the
first command Iref1. In this case, the second command Iref2 is
determined so that avalanche current will not be excessive. The
second command Iref2 may have a value different from the first
command Iref1.
[0155] On the other hand, a current correction unit 51 accepts
inputs of the input voltage Vin and the capacitive load voltage Vc
and outputs a correction value to be added to the second command
Iref2. An addition unit 52 adds the correction value outputted from
the current correction unit 51 to the second command Iref2 and
outputs a second corrected command Iref2' (corrected second
command). The relationship of the input voltage Vin and the
capacitive load voltage Vc relative to the correction value to be
added to the second command Iref2 may be obtained from calculation.
Alternatively, the relationship may be obtained on the basis of a
predetermined table stored in a memory.
[0156] In the second mode controlled on the basis of the second
command Iref2, the Duty value of the first switching element Q1 is
fixed to 50% and the Duty value of the second switching element Q2
is changed. Specifically, in the second mode, the Duty value of the
second switching element Q2 is changed in such a way that the value
of the reactor current IL will be the second corrected command
Iref2' in the period .alpha. in which the first and second
switching elements Q1 and Q2 are in an ON-state. Further, in the
second mode, the Duty value of the second switching element Q2 is
changed in such a way that the value of the reactor current IL will
be the second command Iref2 in the period .beta. in which the first
switching element Q1 is in an ON-state and the second switching
element Q2 is in an OFF-state.
[0157] Referring to FIGS. 13A to 13C, the relationship between the
second command Iref2 and the second corrected command Iref2' will
be described.
[0158] FIG. 13A shows the reactor current IL when the value of the
input voltage Vin is larger than a value obtained by dividing the
capacitive load voltage Vc by a turn ratio N. In this case, the
reactor current IL increases in the period .beta. in which the
first switching element Q1 is in an ON-state and the second
switching element Q2 is in an OFF-state. Therefore, when the value
of the reactor current IL at a time point of turning OFF the second
switching element Q2 is taken as the second command Iref2, the
reactor current IL is likely to be excessive. In this regard, in
the second mode, at a time point of turning OFF the first switching
element Q1, the period .alpha. in which the second switching
element Q2 is in an ON-state is set in such a way that the value of
the reactor current IL will be the second command Iref2.
[0159] FIG. 13B shows the reactor current IL when the value
obtained by dividing the capacitive load voltage Vc by a turn ratio
N is equal to the value of the input voltage Vin. In this case, in
the period p, the reactor current IL neither increases nor
decreases. Therefore, the second command Iref2 and the second
corrected command Iref2' have the same value.
[0160] FIG. 13C shows the reactor current IL when the value of the
input voltage Vin is smaller than the value obtained by dividing
the capacitive load voltage Vc by a turn ratio N. In this case, in
the period .beta., the reactor current IL decreases. Therefore,
when the value of the reactor current IL at a time point of turning
OFF the second switching element Q2 is taken as the second command
Iref2, charge time increases with the decrease of the reactor
current IL in the period 3. In this regard, in the second mode, the
period .alpha. in which the second switching element Q2 is in an
ON-state is set in such a way that the value of the reactor current
IL will be the second command Iref2 at the time point of turning
OFF the first switching element Q1.
[0161] Referring to FIG. 12 again, a feedback control unit 53
accepts an input of the third command Iref3. The third command
Iref3 has a value larger than the first and second commands Iref1
and Iref2. Further, the feedback control unit 53 acquires an
average IL_ave, which is an actual current of the reactor current
IL. The average IL_ave is obtained by accumulating the reactor
current IL detected by the current detecting means 19 in a
predetermined period and averaging the values. An addition unit 54
accepts inputs of the third command Iref3 and the average IL_ave to
obtain a difference between the third command Iref3 and the average
IL_ave. The difference value outputted from the addition unit 54 is
inputted to a PI controller 55 and outputted to a limiter 56. When
an output value of the PI controller 55 is larger than a
predetermined upper limit, the limiter 56 limits the output value
to the upper limit. An adder 57 adds an output value from the
limiter 56 to the third command Iref3. As a result, the feedback
control unit 53 outputs the third command Iref3 to which the output
value of the limiter 56 has been added.
[0162] On the other hand, a current correction unit 58 accepts
inputs of the input voltage Vin and the capacitive load voltage Vc
and outputs a correction value to be added to the third command
Iref3. An addition unit 59 adds the correction value outputted from
the current correction unit 58 to the third command Iref3 and
outputs a third corrected command Iref3' (corrected third command).
The correction is made for the following reasons. In the third
mode, similar to the second mode, in the period .beta. in which the
first switching element Q1 is in an ON-state and the second
switching element Q2 is in an OFF-state, decrease of the reactor
current IL changes depending on the input voltage Vin and the
capacitive load voltage Vc. Therefore, in the third mode, a
correction value taking account of the decrease is required to be
added. Further, in the third mode, a phenomenon caused by a slope
compensation unit 73 (divergence between the third command Iref3
and the average IL_ave) described later is required to be
corrected.
[0163] A mode selection unit 60 accepts inputs of the first command
Iref1, the second corrected command Iref2', and the third corrected
command Iref3' that are outputted from the constant current control
unit 50. Further, the mode selection unit 60 accepts an input of
the capacitive load voltage Vc and compares the capacitive load
voltage Vc with the first and second predetermined values V1 and
V2. The mode selection unit 60 selects one command to be outputted
from among the three candidates of the first command Iref1, the
second corrected command Iref2', and the third corrected command
Iref3' on the basis of the result of the comparison, and outputs
the selected command.
[0164] A peak current control unit 70 accepts an input of the
command (any one command of the first command Iref1, the second
corrected command Iref2', and the third corrected command Iref3')
outputted from the mode selection unit 60. A DA converter 71
converts the command inputted from the mode selection unit 60 to an
analog value and outputs the converted value to a negative terminal
of a comparator 72.
[0165] On the other hand, the slope compensation unit 73 generates
a slope signal on the basis of a resistor value and inputs the
generated slope signal into a DA converter 74. The slope signal is
a sawtooth wave signal that linearly and monotonically increases
from 0 A in each control cycle. Then, the DA converter 74 converts
the inputted slope signal to an analog waveform and outputs the
analog waveform to an addition unit 75. The addition unit 75 adds
up the inputted reactor current IL and the slope signal after
analog conversion, and outputs the added value to a positive
terminal of the comparator 72. In the slope compensation unit 73,
an analog waveform of the slope signal may be directly generated
and the generated slope signal may be outputted to the addition
unit 75 without being interposed by the DA converter 74.
[0166] The slope compensation unit 73 allows the value of the slope
signal to be zero in the first and second modes and outputs a
sawtooth wave slope signal in the third mode. The reason why the
value of the slope signal is rendered to be zero is as follows. At
a time point of turning OFF both of the first and second switching
elements Q1 and Q2, the reactor current IL becomes zero in the
first and second modes. As a result, a phenomenon of subharmonic
oscillation does not occur in the first and second modes.
[0167] The comparator 72 compares an input value of the negative
terminal with an input value of the positive terminal. The negative
terminal of the comparator 72 accepts an input of a command after
analog conversion outputted from the DA converter 71 (any one of
the first command Iref1, the second corrected command Iref2', and
the third corrected command Iref3' after analog conversion). On the
other hand, the positive terminal of the comparator 72 accepts an
input of the addition value outputted from the adder 75 (value
obtained by adding the slope signal after analog conversion to the
reactor current IL). Thus, the comparator 72 compares any one of
the first command Iref1, the second corrected command Iref2', and
the third corrected command Iref3' after analog conversion, with
the value obtained by adding the slope signal after analog
conversion to the reactor current IL. Then, when the input value of
the positive terminal is smaller than the input value of the
negative terminal, the comparator 72 outputs a high signal to an S
terminal of an RS flip-flop 77. In contrast, when the input value
of the positive terminal is larger than the input value of the
negative terminal, the comparator 72 outputs a low signal to the S
terminal of the RS flip-flop 77. The RS flip-flop 77 has an R
terminal that accepts an input of a clock signal from a clock
76.
[0168] In the first mode, the RS flip-flop 77 outputs a signal for
turning ON one of the first and second switching elements Q1 and Q2
and turning OFF the other switching element, when the input signal
is high. In contrast, in the first mode, the RS flip-flop 77
outputs a signal for turning OFF both of the first and second
switching elements Q1 and Q2, when the input signal is low.
[0169] In the second mode, the RS flip-flop 77 outputs a signal for
turning ON both of the first and second switching elements Q1 and
Q2, when the input signal is high. In contrast, when the input
signal is low in the second mode, the RS flip-flop 77 outputs a
signal for turning ON the first switching element Q1 and turning
OFF the second switching element Q2 until the Duty value exceeds
50% (in a half of the control cycle). Then, when the Duty value
exceeds 50%, the RS flip-flop 77 outputs a signal for turning OFF
both of the first and second switching elements Q1 and Q2. When the
input signal is low, a process of a Duty limitation unit 78 may
take over the control of keeping an ON-state of the first switching
element Q1 until the Duty value exceeds 50%.
[0170] In the third mode, when the input signal is high, the RS
flip-flop 77 outputs a signal for turning ON both of the first and
second switching elements Q1 and Q2. In contrast, in the third
mode, when the input signal is low, the RS flip-flop 77 outputs a
signal for turning ON one of the first and second switching
elements Q1 and Q2 and turning OFF the other switching element.
[0171] The Duty limitation unit 78 sets an upper limit and a lower
limit of the Duty value to the signal outputted from the RS
flip-flop 77 and outputs the set signal to the driving circuit 18
that drives the first and second switching elements Q1 and Q2.
Specifically, in the first mode, the Duty limitation unit 78 sets
an upper limit of the Duty value for each of the first and second
switching elements Q1 and Q2 to a value of not more than 50% to
prevent overlap of the ON-state period of the in the first
switching element Q1 with the ON-state period of the second
switching element Q2. In the second mode as well, the Duty
limitation unit 78 sets the Duty value of the first switching
element Q1 to 50% as described above. Therefore, in the second
mode, the Duty limitation unit 78 sets the upper limit so that the
Duty value of the second switching element Q2 does not become
larger than the Duty value of the first switching element Q1. In
the third mode, the Duty limitation unit 78 sets the lower limit of
the Duty value for each of the first and second switching elements
Q1 and Q2 to a value more than 50% to prevent overlap of the
ON-state period of the first switching element Q1 with the ON-state
period of the second switching element Q2.
[0172] With the above configuration, the power conversion apparatus
7 of the present embodiment exhibits the following advantageous
effects in addition to those similar to the first embodiment.
[0173] In the power conversion apparatus 7 of the present
embodiment, the peak current control unit 70 performs constant
current control using the first command Iref1, the second corrected
command Iref2', and the third corrected command Iref3' that are
inputted from the constant current control unit 50. Thus, in the
power conversion apparatus 7 of the present embodiment, robustness
against overcurrent can be improved such as when the input voltage
Vin alters.
[0174] In the power conversion apparatus 7 of the present
embodiment, under the peak current control of the second mode, the
Duty value of one of the switching elements is fixed and the
ON-state period of the other switching element is changed.
Therefore, in the power conversion apparatus 7, the peak current
control is simplified in comparison with the control under which
both of two Duty values corresponding to the respective first and
second switching elements Q1 and Q2 are changed. Thus, in the power
conversion apparatus 7 of the present embodiment, robustness
against overcurrent can be improved.
[0175] In the power conversion apparatus 7 of the present
embodiment, the fixed Duty value is not more than 50% in the second
mode, which leads to making longer the period .gamma. in which both
of the first and second switching elements Q1 and Q2 are in an
OFF-state. Thus, in the power conversion apparatus 7 of the present
embodiment, excitation current passing through the transformer Tr
is decreased in the period .gamma., and magnetic deflection or
saturation of the transformer Tr is minimized.
[0176] In the power conversion apparatus 7 of the present
embodiment, the first and third commands Iref1 and Iref3 are
rendered to be divergent values, and the second and third commands
Iref2 and Iref3 are rendered to be divergent values. Thus, in the
power conversion apparatus 7, the reactor current IL does not
become excessive in the first and second modes. Therefore, in the
power conversion apparatus 7, when both of the first and second
switching elements Q1 and Q2 are turned OFF, the avalanche current
is not excessively increased, and thus failure or breakage of the
first and second switching elements Q1 and Q2 is minimized.
Further, in the power conversion apparatus 7 of the present
embodiment, the third command Iref3 is ensured to have a large
value in the third mode, and thus the charge time can be
shortened.
[0177] In the power conversion apparatus 7 of the present
embodiment, under the constant current control of the second mode,
the second command Iref2 is corrected using the capacitive load
voltage Vc and the input voltage Vin to obtain the second corrected
command Iref2'. In the power conversion apparatus 7, the second
corrected command Iref2' is used for determining an ON-state period
of the second switching element Q2. Thus, in the power conversion
apparatus 7, when the value of the input voltage Vin is larger than
the value obtained by dividing the capacitive load voltage Vc by a
turn ratio N, the second corrected command Iref2' becomes smaller
than the second command Iref2, and after increase of the reactor
current IL in the period .beta., the second corrected command
Iref2' serves as the second command Iref2. Therefore, the power
conversion apparatus 7 of the present embodiment minimizes an
excessive increase of avalanche current. In contrast, in the power
conversion apparatus 7, when the value of the input voltage Vin is
smaller than the value obtained by dividing the capacitive load
voltage Vc by a turn ratio N, the second corrected command Iref2'
becomes larger than the second command Iref2, and after decrease of
the reactor current IL in the period .beta., the second corrected
command Iref2' serves as the second command Iref2. Therefore, in
the power conversion apparatus 7 of the present embodiment, the
reactor current IL is increased in the period a, and thus the
charge period can be shortened.
Modifications
[0178] In the first embodiment, when the second mode is switched to
the third mode, the first predetermined value V1 is set in such a
way that the output voltage Vout of the transformer Tr is equal to
the capacitive load voltage Vc. Alternatively, however, the setting
of the first predetermined value V1 may be corrected using a
predetermined correction value .DELTA.V1 and the first
predetermined value V1 may be set using the following equation
(10).
V1=N.times.Vin/(2.times.(1-Duty0))-.DELTA.V1 (10)
[0179] In fact, if there is a difference between the output voltage
Vout of the transformer Tr and the capacitive load voltage Vc, high
current is not necessarily caused immediately. That is, the
difference between the actual output voltage Vout and a theoretical
value is caused due to the capacitive load 30, the wiring, the
resistance of each coil, the loss of each switching element, the
difference between the command of each PWM signal and the actual
Duty value, and the like. Therefore, actually, the current value
will not become infinite. When the current value is smaller than a
current resistance of an element in the circuit, the occurrence is
tolerated.
[0180] When the control of the third mode is performed, as
described above, the charging rate for the capacitive load 30 can
be increased. Accordingly, in the present modification, a positive
correction value .DELTA.V1 is subtracted from the first
predetermined value V1, and the control of the third mode is
started earlier. Thus, in comparison with the case of using a
theoretical value as the first predetermined value V1, the charging
rate for the capacitive load 30 can be increased.
[0181] The correction value .DELTA.V1 may be a negative value. In
this case, the first predetermined value V1 becomes large and
transition from the second mode to the third mode is delayed, and
thus the charging rate for the capacitive load 30 is lowered. On
the other hand, in this case, the current that is caused due to the
difference between the output voltage Vout of the transformer Tr
and the capacitive load voltage Vc can be minimized even more.
Accordingly, a circuit configuration applying less load on an
element in the circuit can be achieved.
[0182] In the first embodiment, in performing the control of the
third mode, Duty3 is set in such a way that the output voltage Vout
of the transformer Tr is equal to the capacitive load voltage Vc.
Alternatively, however, Duty3 may be set by correcting the
capacitive load voltage Vc using a predetermined correction value
.DELTA.Vc, as in the following equation (11).
Duty3=1-N.times.Vin/(2.times.(Vc+.DELTA.Vc)) (11)
[0183] As described above, in fact, if there is a difference
between the output voltage Vout of the transformer Tr and the
capacitive load voltage Vc, high current is not necessarily caused
immediately. In this regard, in calculating Duty3 in the present
modification, the correction value .DELTA.Vc is added to the
capacitive load voltage Vc, thereby making Duty3 larger than the
theoretical value. Thus, in the present modification, the time of
applying the input voltage Vin to the choke coil 11 can be made
longer, and the current used for charge can be increased. As a
result, the charging rate can be increased more. The correction
value .DELTA.Vc may be the same value as or may be a different from
the correction value .DELTA.V1. The correction value .DELTA.Vc may
be changed in conformity with the increase of the capacitive load
voltage Vc.
[0184] The correction value .DELTA.V1 may be a negative value. In
this case, the value of Duty3 is decreased and the period .alpha.
of increasing the current of the choke coil 11 is shortened, and
thus the charging rate for the capacitive load 30 is decreased. On
the other hand, in this case, the current that is caused due to the
difference between the output voltage Vout of the transformer Tr
and the capacitive load voltage Vc can be mitigated further,
thereby achieving a circuit configuration imposing no load on the
an element in the circuit.
[0185] In the first embodiment, the first mode is taken as the case
where the output voltage Vout is not larger than the second
predetermined value V2, the second mode is taken as the case where
the output voltage Vout is larger than the second predetermined
value V2 but not larger than the first predetermined value V1, and
the third mode is taken as the case where the output voltage Vout
is larger than the first predetermined value V1. However, the
control method by the first, second and third modes is not limited
to this. Specifically, the first mode may be taken as the case
where the output voltage Vout is smaller than the second
predetermined value V2, the second mode may be taken as the case
where the output voltage Vout is not smaller than the second
predetermined value V2 but smaller than the first predetermined
value V1, and the third mode may be taken as the case where the
output voltage Vout is not smaller than the first predetermined
value V1. This control method is applied to the third
embodiment.
[0186] In the first embodiment, the control cycles of the first,
second and third modes have an equal value. Alternatively, the
control cycles may be different from each other in these modes.
That is, in each mode, the control cycle of the first PWM signal
only has to be equal to the control cycle of the second PWM signal.
In the second embodiment, the control cycles of the first and third
modes may have a different value. This method of setting control
cycle is applied to the third embodiment.
[0187] In each embodiment, it is preferable to set the length T1 of
an ON-state period in such a way that the choke coil current
becomes zero when the period .gamma. of the first mode has expired.
However, setting of the length T1 is not necessarily limited to
this. When the length T1 of the ON-state period is set in such a
way that the choke coil current does not become zero at the
expiration of the period .gamma., the choke coil current gradually
increases due to the repetition of the control of the first mode.
In this case, the length T1 of the ON-state period may only have to
be set in such a way that the gradually increasing choke coil
current does not exceed the rated current values of the first and
second switching elements Q1 and Q2.
[0188] In the first and third embodiments it is preferable to set
the lengths T2h and T2l of the ON-state period in such a way that
the choke coil current becomes zero at the expiration of the period
.gamma. of the second mode. However, setting of the lengths T2h and
T2l is not necessarily limited to this. When the lengths T2h and
T2l of the ON-state period are set in such a way that the choke
coil current does not become zero at the expiration of the period
.gamma., the choke coil current gradually increases due to the
repetition of the control of the second mode. In this case, the
lengths T2h and T2l of the ON-state period may only have to be set
in such a way that the gradually increasing choke coil current does
not exceed the rated current values of the first and second
switching elements Q1 and Q2.
[0189] In each embodiment, it is preferable to set the length T3 of
the ON-state period in such a way that the increase of the choke
coil current in the period .alpha. will be equal to the decrease of
the choke coil current in the period .beta.. However, setting of
the length T3 is not necessarily limited to this. When the length
T3 of the ON-state period is set in such a way that the decrease of
the choke coil current in the period .beta. is smaller than the
increase of the choke coil current in the period a, the choke coil
current gradually increases due to the repetition of the control of
the third mode. In this case, the length T3 of the ON-state period
may only have to be set in such a way that the gradually increasing
choke coil current does not exceed the rated current values of the
first and second switching elements Q1 and Q2.
[0190] In the first embodiment, in the first mode, one control
cycle is defined to be from the time point of turning ON the first
switching element Q1 until the time point of turning ON the first
switching element Q1 next time. However, the definition of a
control cycle is not limited to this. For example, one control
cycle may defined to be from a time point of turning OFF the first
switching element Q1 until a time point of turning ON the first
switching element Q1 next time. The definition of a control cycle
is applied to other modes. The definition of a control cycle in the
fifth embodiment is not limited to the above example. In the fifth
embodiment, for example, in the control of the first mode shown in
FIG. 9A, one control cycle may be defined as a control cycle
including one period .beta. and one period .gamma. which each
correspond to a 1/4 control cycle. In this case as well, the time
point of starting the control cycle may be the time point of
turning OFF the switching element.
[0191] The seventh embodiment is configured to correct the second
command Iref2. However, the seventh embodiment may be configured
not to perform the correction. In this case, the value of the
reactor current IL serves as the second command Iref2 at the time
point of turning OFF one of the first and second switching elements
Q1 and Q2. When such control is performed, the ON-state period of a
switching element having a shorter ON-state period may be fixed and
the ON-state period of the other switching element may be changed,
or the ON-state periods of both of the switching elements may be
variable.
[0192] similar to the second embodiment, the seventh embodiment may
be configured not to perform the control of the second mode.
[0193] In each embodiment, the power conversion apparatus is
provided to a hybrid vehicle. However, the power conversion
apparatus can be applied to objects other than hybrid vehicles.
Further, in each embodiment, the DCDC converter 10 is ensured to
perform bidirectional supply/reception of power. However, the DCDC
converter 10 may be ensured to perform power supply only from the
first coil L1 side to the second coil L2 side. In that case, the
bridge circuit 14 may be used as a diode bridge circuit.
DESCRIPTION OF REFERENCE SIGNS
[0194] 1, 3, 7 . . . power conversion apparatus, 10 . . . DCDC
converter, 11 . . . choke coil, 12 . . . predetermined connecting
point, 13 . . . center tap, 14 . . . bridge circuit, 15 . . . input
voltage detecting means, 16 . . . capacitive load voltage detecting
means, 17 . . . pulse generation unit, 19 . . . current detecting
means, 20 . . . secondary battery, 30 . . . capacitive load, 73 . .
. slope compensation unit, 75 . . . addition unit, L1 . . . first
coil, L2 . . . second coil, Q1 . . . first switching element, Q2 .
. . second switching element.
* * * * *